[RFC,07/86] Revert "livepatch,sched: Add livepatch task switching to cond_resched()"
Commit Message
This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8.
Note that removing this commit reintroduces "live patches failing to
complete within a reasonable amount of time due to CPU-bound kthreads."
Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and
existence of cond_resched() so this will need an alternate fix.
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
include/linux/livepatch.h | 1 -
include/linux/livepatch_sched.h | 29 ---------
include/linux/sched.h | 20 ++----
kernel/livepatch/core.c | 1 -
kernel/livepatch/transition.c | 107 +++++---------------------------
kernel/sched/core.c | 64 +++----------------
6 files changed, 28 insertions(+), 194 deletions(-)
delete mode 100644 include/linux/livepatch_sched.h
Comments
On Tue, 7 Nov 2023 13:56:53 -0800
Ankur Arora <ankur.a.arora@oracle.com> wrote:
> This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8.
>
> Note that removing this commit reintroduces "live patches failing to
> complete within a reasonable amount of time due to CPU-bound kthreads."
>
> Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and
> existence of cond_resched() so this will need an alternate fix.
>
Then it would probably be a good idea to Cc the live patching maintainers!
-- Steve
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> ---
> include/linux/livepatch.h | 1 -
> include/linux/livepatch_sched.h | 29 ---------
> include/linux/sched.h | 20 ++----
> kernel/livepatch/core.c | 1 -
> kernel/livepatch/transition.c | 107 +++++---------------------------
> kernel/sched/core.c | 64 +++----------------
> 6 files changed, 28 insertions(+), 194 deletions(-)
> delete mode 100644 include/linux/livepatch_sched.h
>
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index 9b9b38e89563..293e29960c6e 100644
> --- a/include/linux/livepatch.h
> +++ b/include/linux/livepatch.h
> @@ -13,7 +13,6 @@
> #include <linux/ftrace.h>
> #include <linux/completion.h>
> #include <linux/list.h>
> -#include <linux/livepatch_sched.h>
>
> #if IS_ENABLED(CONFIG_LIVEPATCH)
>
> diff --git a/include/linux/livepatch_sched.h b/include/linux/livepatch_sched.h
> deleted file mode 100644
> index 013794fb5da0..000000000000
> --- a/include/linux/livepatch_sched.h
> +++ /dev/null
> @@ -1,29 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0-or-later */
> -#ifndef _LINUX_LIVEPATCH_SCHED_H_
> -#define _LINUX_LIVEPATCH_SCHED_H_
> -
> -#include <linux/jump_label.h>
> -#include <linux/static_call_types.h>
> -
> -#ifdef CONFIG_LIVEPATCH
> -
> -void __klp_sched_try_switch(void);
> -
> -#if !defined(CONFIG_PREEMPT_DYNAMIC) || !defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> -
> -DECLARE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
> -
> -static __always_inline void klp_sched_try_switch(void)
> -{
> - if (static_branch_unlikely(&klp_sched_try_switch_key))
> - __klp_sched_try_switch();
> -}
> -
> -#endif /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
> -
> -#else /* !CONFIG_LIVEPATCH */
> -static inline void klp_sched_try_switch(void) {}
> -static inline void __klp_sched_try_switch(void) {}
> -#endif /* CONFIG_LIVEPATCH */
> -
> -#endif /* _LINUX_LIVEPATCH_SCHED_H_ */
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 5bdf80136e42..c5b0ef1ecfe4 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -36,7 +36,6 @@
> #include <linux/seqlock.h>
> #include <linux/kcsan.h>
> #include <linux/rv.h>
> -#include <linux/livepatch_sched.h>
> #include <asm/kmap_size.h>
>
> /* task_struct member predeclarations (sorted alphabetically): */
> @@ -2087,9 +2086,6 @@ extern int __cond_resched(void);
>
> #if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
>
> -void sched_dynamic_klp_enable(void);
> -void sched_dynamic_klp_disable(void);
> -
> DECLARE_STATIC_CALL(cond_resched, __cond_resched);
>
> static __always_inline int _cond_resched(void)
> @@ -2098,7 +2094,6 @@ static __always_inline int _cond_resched(void)
> }
>
> #elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> -
> extern int dynamic_cond_resched(void);
>
> static __always_inline int _cond_resched(void)
> @@ -2106,25 +2101,20 @@ static __always_inline int _cond_resched(void)
> return dynamic_cond_resched();
> }
>
> -#else /* !CONFIG_PREEMPTION */
> +#else
>
> static inline int _cond_resched(void)
> {
> - klp_sched_try_switch();
> return __cond_resched();
> }
>
> -#endif /* PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
> +#endif /* CONFIG_PREEMPT_DYNAMIC */
>
> -#else /* CONFIG_PREEMPTION && !CONFIG_PREEMPT_DYNAMIC */
> +#else
>
> -static inline int _cond_resched(void)
> -{
> - klp_sched_try_switch();
> - return 0;
> -}
> +static inline int _cond_resched(void) { return 0; }
>
> -#endif /* !CONFIG_PREEMPTION || CONFIG_PREEMPT_DYNAMIC */
> +#endif /* !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) */
>
> #define cond_resched() ({ \
> __might_resched(__FILE__, __LINE__, 0); \
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 61328328c474..fc851455740c 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -33,7 +33,6 @@
> *
> * - klp_ftrace_handler()
> * - klp_update_patch_state()
> - * - __klp_sched_try_switch()
> */
> DEFINE_MUTEX(klp_mutex);
>
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index e54c3d60a904..70bc38f27af7 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -9,7 +9,6 @@
>
> #include <linux/cpu.h>
> #include <linux/stacktrace.h>
> -#include <linux/static_call.h>
> #include "core.h"
> #include "patch.h"
> #include "transition.h"
> @@ -27,25 +26,6 @@ static int klp_target_state = KLP_UNDEFINED;
>
> static unsigned int klp_signals_cnt;
>
> -/*
> - * When a livepatch is in progress, enable klp stack checking in
> - * cond_resched(). This helps CPU-bound kthreads get patched.
> - */
> -#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> -
> -#define klp_cond_resched_enable() sched_dynamic_klp_enable()
> -#define klp_cond_resched_disable() sched_dynamic_klp_disable()
> -
> -#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
> -
> -DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
> -EXPORT_SYMBOL(klp_sched_try_switch_key);
> -
> -#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
> -#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
> -
> -#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
> -
> /*
> * This work can be performed periodically to finish patching or unpatching any
> * "straggler" tasks which failed to transition in the first attempt.
> @@ -194,8 +174,8 @@ void klp_update_patch_state(struct task_struct *task)
> * barrier (smp_rmb) for two cases:
> *
> * 1) Enforce the order of the TIF_PATCH_PENDING read and the
> - * klp_target_state read. The corresponding write barriers are in
> - * klp_init_transition() and klp_reverse_transition().
> + * klp_target_state read. The corresponding write barrier is in
> + * klp_init_transition().
> *
> * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
> * of func->transition, if klp_ftrace_handler() is called later on
> @@ -363,44 +343,6 @@ static bool klp_try_switch_task(struct task_struct *task)
> return !ret;
> }
>
> -void __klp_sched_try_switch(void)
> -{
> - if (likely(!klp_patch_pending(current)))
> - return;
> -
> - /*
> - * This function is called from cond_resched() which is called in many
> - * places throughout the kernel. Using the klp_mutex here might
> - * deadlock.
> - *
> - * Instead, disable preemption to prevent racing with other callers of
> - * klp_try_switch_task(). Thanks to task_call_func() they won't be
> - * able to switch this task while it's running.
> - */
> - preempt_disable();
> -
> - /*
> - * Make sure current didn't get patched between the above check and
> - * preempt_disable().
> - */
> - if (unlikely(!klp_patch_pending(current)))
> - goto out;
> -
> - /*
> - * Enforce the order of the TIF_PATCH_PENDING read above and the
> - * klp_target_state read in klp_try_switch_task(). The corresponding
> - * write barriers are in klp_init_transition() and
> - * klp_reverse_transition().
> - */
> - smp_rmb();
> -
> - klp_try_switch_task(current);
> -
> -out:
> - preempt_enable();
> -}
> -EXPORT_SYMBOL(__klp_sched_try_switch);
> -
> /*
> * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
> * Kthreads with TIF_PATCH_PENDING set are woken up.
> @@ -507,8 +449,7 @@ void klp_try_complete_transition(void)
> return;
> }
>
> - /* Done! Now cleanup the data structures. */
> - klp_cond_resched_disable();
> + /* we're done, now cleanup the data structures */
> patch = klp_transition_patch;
> klp_complete_transition();
>
> @@ -560,8 +501,6 @@ void klp_start_transition(void)
> set_tsk_thread_flag(task, TIF_PATCH_PENDING);
> }
>
> - klp_cond_resched_enable();
> -
> klp_signals_cnt = 0;
> }
>
> @@ -617,9 +556,8 @@ void klp_init_transition(struct klp_patch *patch, int state)
> * see a func in transition with a task->patch_state of KLP_UNDEFINED.
> *
> * Also enforce the order of the klp_target_state write and future
> - * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() and
> - * __klp_sched_try_switch() don't set a task->patch_state to
> - * KLP_UNDEFINED.
> + * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
> + * set a task->patch_state to KLP_UNDEFINED.
> */
> smp_wmb();
>
> @@ -655,10 +593,14 @@ void klp_reverse_transition(void)
> klp_target_state == KLP_PATCHED ? "patching to unpatching" :
> "unpatching to patching");
>
> + klp_transition_patch->enabled = !klp_transition_patch->enabled;
> +
> + klp_target_state = !klp_target_state;
> +
> /*
> * Clear all TIF_PATCH_PENDING flags to prevent races caused by
> - * klp_update_patch_state() or __klp_sched_try_switch() running in
> - * parallel with the reverse transition.
> + * klp_update_patch_state() running in parallel with
> + * klp_start_transition().
> */
> read_lock(&tasklist_lock);
> for_each_process_thread(g, task)
> @@ -668,28 +610,9 @@ void klp_reverse_transition(void)
> for_each_possible_cpu(cpu)
> clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
>
> - /*
> - * Make sure all existing invocations of klp_update_patch_state() and
> - * __klp_sched_try_switch() see the cleared TIF_PATCH_PENDING before
> - * starting the reverse transition.
> - */
> + /* Let any remaining calls to klp_update_patch_state() complete */
> klp_synchronize_transition();
>
> - /*
> - * All patching has stopped, now re-initialize the global variables to
> - * prepare for the reverse transition.
> - */
> - klp_transition_patch->enabled = !klp_transition_patch->enabled;
> - klp_target_state = !klp_target_state;
> -
> - /*
> - * Enforce the order of the klp_target_state write and the
> - * TIF_PATCH_PENDING writes in klp_start_transition() to ensure
> - * klp_update_patch_state() and __klp_sched_try_switch() don't set
> - * task->patch_state to the wrong value.
> - */
> - smp_wmb();
> -
> klp_start_transition();
> }
>
> @@ -703,9 +626,9 @@ void klp_copy_process(struct task_struct *child)
> * the task flag up to date with the parent here.
> *
> * The operation is serialized against all klp_*_transition()
> - * operations by the tasklist_lock. The only exceptions are
> - * klp_update_patch_state(current) and __klp_sched_try_switch(), but we
> - * cannot race with them because we are current.
> + * operations by the tasklist_lock. The only exception is
> + * klp_update_patch_state(current), but we cannot race with
> + * that because we are current.
> */
> if (test_tsk_thread_flag(current, TIF_PATCH_PENDING))
> set_tsk_thread_flag(child, TIF_PATCH_PENDING);
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0e8764d63041..b43fda3c5733 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8597,7 +8597,6 @@ EXPORT_STATIC_CALL_TRAMP(might_resched);
> static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
> int __sched dynamic_cond_resched(void)
> {
> - klp_sched_try_switch();
> if (!static_branch_unlikely(&sk_dynamic_cond_resched))
> return 0;
> return __cond_resched();
> @@ -8746,17 +8745,13 @@ int sched_dynamic_mode(const char *str)
> #error "Unsupported PREEMPT_DYNAMIC mechanism"
> #endif
>
> -DEFINE_MUTEX(sched_dynamic_mutex);
> -static bool klp_override;
> -
> -static void __sched_dynamic_update(int mode)
> +void sched_dynamic_update(int mode)
> {
> /*
> * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
> * the ZERO state, which is invalid.
> */
> - if (!klp_override)
> - preempt_dynamic_enable(cond_resched);
> + preempt_dynamic_enable(cond_resched);
> preempt_dynamic_enable(might_resched);
> preempt_dynamic_enable(preempt_schedule);
> preempt_dynamic_enable(preempt_schedule_notrace);
> @@ -8764,79 +8759,36 @@ static void __sched_dynamic_update(int mode)
>
> switch (mode) {
> case preempt_dynamic_none:
> - if (!klp_override)
> - preempt_dynamic_enable(cond_resched);
> + preempt_dynamic_enable(cond_resched);
> preempt_dynamic_disable(might_resched);
> preempt_dynamic_disable(preempt_schedule);
> preempt_dynamic_disable(preempt_schedule_notrace);
> preempt_dynamic_disable(irqentry_exit_cond_resched);
> - if (mode != preempt_dynamic_mode)
> - pr_info("Dynamic Preempt: none\n");
> + pr_info("Dynamic Preempt: none\n");
> break;
>
> case preempt_dynamic_voluntary:
> - if (!klp_override)
> - preempt_dynamic_enable(cond_resched);
> + preempt_dynamic_enable(cond_resched);
> preempt_dynamic_enable(might_resched);
> preempt_dynamic_disable(preempt_schedule);
> preempt_dynamic_disable(preempt_schedule_notrace);
> preempt_dynamic_disable(irqentry_exit_cond_resched);
> - if (mode != preempt_dynamic_mode)
> - pr_info("Dynamic Preempt: voluntary\n");
> + pr_info("Dynamic Preempt: voluntary\n");
> break;
>
> case preempt_dynamic_full:
> - if (!klp_override)
> - preempt_dynamic_disable(cond_resched);
> + preempt_dynamic_disable(cond_resched);
> preempt_dynamic_disable(might_resched);
> preempt_dynamic_enable(preempt_schedule);
> preempt_dynamic_enable(preempt_schedule_notrace);
> preempt_dynamic_enable(irqentry_exit_cond_resched);
> - if (mode != preempt_dynamic_mode)
> - pr_info("Dynamic Preempt: full\n");
> + pr_info("Dynamic Preempt: full\n");
> break;
> }
>
> preempt_dynamic_mode = mode;
> }
>
> -void sched_dynamic_update(int mode)
> -{
> - mutex_lock(&sched_dynamic_mutex);
> - __sched_dynamic_update(mode);
> - mutex_unlock(&sched_dynamic_mutex);
> -}
> -
> -#ifdef CONFIG_HAVE_PREEMPT_DYNAMIC_CALL
> -
> -static int klp_cond_resched(void)
> -{
> - __klp_sched_try_switch();
> - return __cond_resched();
> -}
> -
> -void sched_dynamic_klp_enable(void)
> -{
> - mutex_lock(&sched_dynamic_mutex);
> -
> - klp_override = true;
> - static_call_update(cond_resched, klp_cond_resched);
> -
> - mutex_unlock(&sched_dynamic_mutex);
> -}
> -
> -void sched_dynamic_klp_disable(void)
> -{
> - mutex_lock(&sched_dynamic_mutex);
> -
> - klp_override = false;
> - __sched_dynamic_update(preempt_dynamic_mode);
> -
> - mutex_unlock(&sched_dynamic_mutex);
> -}
> -
> -#endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
> -
> static int __init setup_preempt_mode(char *str)
> {
> int mode = sched_dynamic_mode(str);
Steven Rostedt <rostedt@goodmis.org> writes:
> On Tue, 7 Nov 2023 13:56:53 -0800
> Ankur Arora <ankur.a.arora@oracle.com> wrote:
>
>> This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8.
>>
>> Note that removing this commit reintroduces "live patches failing to
>> complete within a reasonable amount of time due to CPU-bound kthreads."
>>
>> Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and
>> existence of cond_resched() so this will need an alternate fix.
>>
>
> Then it would probably be a good idea to Cc the live patching maintainers!
Indeed. Could have sworn that I had. But clearly not.
Apologies and thanks for adding them.
>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>> ---
>> include/linux/livepatch.h | 1 -
>> include/linux/livepatch_sched.h | 29 ---------
>> include/linux/sched.h | 20 ++----
>> kernel/livepatch/core.c | 1 -
>> kernel/livepatch/transition.c | 107 +++++---------------------------
>> kernel/sched/core.c | 64 +++----------------
>> 6 files changed, 28 insertions(+), 194 deletions(-)
>> delete mode 100644 include/linux/livepatch_sched.h
>>
>> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
>> index 9b9b38e89563..293e29960c6e 100644
>> --- a/include/linux/livepatch.h
>> +++ b/include/linux/livepatch.h
>> @@ -13,7 +13,6 @@
>> #include <linux/ftrace.h>
>> #include <linux/completion.h>
>> #include <linux/list.h>
>> -#include <linux/livepatch_sched.h>
>>
>> #if IS_ENABLED(CONFIG_LIVEPATCH)
>>
>> diff --git a/include/linux/livepatch_sched.h b/include/linux/livepatch_sched.h
>> deleted file mode 100644
>> index 013794fb5da0..000000000000
>> --- a/include/linux/livepatch_sched.h
>> +++ /dev/null
>> @@ -1,29 +0,0 @@
>> -/* SPDX-License-Identifier: GPL-2.0-or-later */
>> -#ifndef _LINUX_LIVEPATCH_SCHED_H_
>> -#define _LINUX_LIVEPATCH_SCHED_H_
>> -
>> -#include <linux/jump_label.h>
>> -#include <linux/static_call_types.h>
>> -
>> -#ifdef CONFIG_LIVEPATCH
>> -
>> -void __klp_sched_try_switch(void);
>> -
>> -#if !defined(CONFIG_PREEMPT_DYNAMIC) || !defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
>> -
>> -DECLARE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
>> -
>> -static __always_inline void klp_sched_try_switch(void)
>> -{
>> - if (static_branch_unlikely(&klp_sched_try_switch_key))
>> - __klp_sched_try_switch();
>> -}
>> -
>> -#endif /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
>> -
>> -#else /* !CONFIG_LIVEPATCH */
>> -static inline void klp_sched_try_switch(void) {}
>> -static inline void __klp_sched_try_switch(void) {}
>> -#endif /* CONFIG_LIVEPATCH */
>> -
>> -#endif /* _LINUX_LIVEPATCH_SCHED_H_ */
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 5bdf80136e42..c5b0ef1ecfe4 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -36,7 +36,6 @@
>> #include <linux/seqlock.h>
>> #include <linux/kcsan.h>
>> #include <linux/rv.h>
>> -#include <linux/livepatch_sched.h>
>> #include <asm/kmap_size.h>
>>
>> /* task_struct member predeclarations (sorted alphabetically): */
>> @@ -2087,9 +2086,6 @@ extern int __cond_resched(void);
>>
>> #if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
>>
>> -void sched_dynamic_klp_enable(void);
>> -void sched_dynamic_klp_disable(void);
>> -
>> DECLARE_STATIC_CALL(cond_resched, __cond_resched);
>>
>> static __always_inline int _cond_resched(void)
>> @@ -2098,7 +2094,6 @@ static __always_inline int _cond_resched(void)
>> }
>>
>> #elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
>> -
>> extern int dynamic_cond_resched(void);
>>
>> static __always_inline int _cond_resched(void)
>> @@ -2106,25 +2101,20 @@ static __always_inline int _cond_resched(void)
>> return dynamic_cond_resched();
>> }
>>
>> -#else /* !CONFIG_PREEMPTION */
>> +#else
>>
>> static inline int _cond_resched(void)
>> {
>> - klp_sched_try_switch();
>> return __cond_resched();
>> }
>>
>> -#endif /* PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
>> +#endif /* CONFIG_PREEMPT_DYNAMIC */
>>
>> -#else /* CONFIG_PREEMPTION && !CONFIG_PREEMPT_DYNAMIC */
>> +#else
>>
>> -static inline int _cond_resched(void)
>> -{
>> - klp_sched_try_switch();
>> - return 0;
>> -}
>> +static inline int _cond_resched(void) { return 0; }
>>
>> -#endif /* !CONFIG_PREEMPTION || CONFIG_PREEMPT_DYNAMIC */
>> +#endif /* !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) */
>>
>> #define cond_resched() ({ \
>> __might_resched(__FILE__, __LINE__, 0); \
>> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
>> index 61328328c474..fc851455740c 100644
>> --- a/kernel/livepatch/core.c
>> +++ b/kernel/livepatch/core.c
>> @@ -33,7 +33,6 @@
>> *
>> * - klp_ftrace_handler()
>> * - klp_update_patch_state()
>> - * - __klp_sched_try_switch()
>> */
>> DEFINE_MUTEX(klp_mutex);
>>
>> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
>> index e54c3d60a904..70bc38f27af7 100644
>> --- a/kernel/livepatch/transition.c
>> +++ b/kernel/livepatch/transition.c
>> @@ -9,7 +9,6 @@
>>
>> #include <linux/cpu.h>
>> #include <linux/stacktrace.h>
>> -#include <linux/static_call.h>
>> #include "core.h"
>> #include "patch.h"
>> #include "transition.h"
>> @@ -27,25 +26,6 @@ static int klp_target_state = KLP_UNDEFINED;
>>
>> static unsigned int klp_signals_cnt;
>>
>> -/*
>> - * When a livepatch is in progress, enable klp stack checking in
>> - * cond_resched(). This helps CPU-bound kthreads get patched.
>> - */
>> -#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
>> -
>> -#define klp_cond_resched_enable() sched_dynamic_klp_enable()
>> -#define klp_cond_resched_disable() sched_dynamic_klp_disable()
>> -
>> -#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
>> -
>> -DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
>> -EXPORT_SYMBOL(klp_sched_try_switch_key);
>> -
>> -#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
>> -#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
>> -
>> -#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
>> -
>> /*
>> * This work can be performed periodically to finish patching or unpatching any
>> * "straggler" tasks which failed to transition in the first attempt.
>> @@ -194,8 +174,8 @@ void klp_update_patch_state(struct task_struct *task)
>> * barrier (smp_rmb) for two cases:
>> *
>> * 1) Enforce the order of the TIF_PATCH_PENDING read and the
>> - * klp_target_state read. The corresponding write barriers are in
>> - * klp_init_transition() and klp_reverse_transition().
>> + * klp_target_state read. The corresponding write barrier is in
>> + * klp_init_transition().
>> *
>> * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
>> * of func->transition, if klp_ftrace_handler() is called later on
>> @@ -363,44 +343,6 @@ static bool klp_try_switch_task(struct task_struct *task)
>> return !ret;
>> }
>>
>> -void __klp_sched_try_switch(void)
>> -{
>> - if (likely(!klp_patch_pending(current)))
>> - return;
>> -
>> - /*
>> - * This function is called from cond_resched() which is called in many
>> - * places throughout the kernel. Using the klp_mutex here might
>> - * deadlock.
>> - *
>> - * Instead, disable preemption to prevent racing with other callers of
>> - * klp_try_switch_task(). Thanks to task_call_func() they won't be
>> - * able to switch this task while it's running.
>> - */
>> - preempt_disable();
>> -
>> - /*
>> - * Make sure current didn't get patched between the above check and
>> - * preempt_disable().
>> - */
>> - if (unlikely(!klp_patch_pending(current)))
>> - goto out;
>> -
>> - /*
>> - * Enforce the order of the TIF_PATCH_PENDING read above and the
>> - * klp_target_state read in klp_try_switch_task(). The corresponding
>> - * write barriers are in klp_init_transition() and
>> - * klp_reverse_transition().
>> - */
>> - smp_rmb();
>> -
>> - klp_try_switch_task(current);
>> -
>> -out:
>> - preempt_enable();
>> -}
>> -EXPORT_SYMBOL(__klp_sched_try_switch);
>> -
>> /*
>> * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
>> * Kthreads with TIF_PATCH_PENDING set are woken up.
>> @@ -507,8 +449,7 @@ void klp_try_complete_transition(void)
>> return;
>> }
>>
>> - /* Done! Now cleanup the data structures. */
>> - klp_cond_resched_disable();
>> + /* we're done, now cleanup the data structures */
>> patch = klp_transition_patch;
>> klp_complete_transition();
>>
>> @@ -560,8 +501,6 @@ void klp_start_transition(void)
>> set_tsk_thread_flag(task, TIF_PATCH_PENDING);
>> }
>>
>> - klp_cond_resched_enable();
>> -
>> klp_signals_cnt = 0;
>> }
>>
>> @@ -617,9 +556,8 @@ void klp_init_transition(struct klp_patch *patch, int state)
>> * see a func in transition with a task->patch_state of KLP_UNDEFINED.
>> *
>> * Also enforce the order of the klp_target_state write and future
>> - * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() and
>> - * __klp_sched_try_switch() don't set a task->patch_state to
>> - * KLP_UNDEFINED.
>> + * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
>> + * set a task->patch_state to KLP_UNDEFINED.
>> */
>> smp_wmb();
>>
>> @@ -655,10 +593,14 @@ void klp_reverse_transition(void)
>> klp_target_state == KLP_PATCHED ? "patching to unpatching" :
>> "unpatching to patching");
>>
>> + klp_transition_patch->enabled = !klp_transition_patch->enabled;
>> +
>> + klp_target_state = !klp_target_state;
>> +
>> /*
>> * Clear all TIF_PATCH_PENDING flags to prevent races caused by
>> - * klp_update_patch_state() or __klp_sched_try_switch() running in
>> - * parallel with the reverse transition.
>> + * klp_update_patch_state() running in parallel with
>> + * klp_start_transition().
>> */
>> read_lock(&tasklist_lock);
>> for_each_process_thread(g, task)
>> @@ -668,28 +610,9 @@ void klp_reverse_transition(void)
>> for_each_possible_cpu(cpu)
>> clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
>>
>> - /*
>> - * Make sure all existing invocations of klp_update_patch_state() and
>> - * __klp_sched_try_switch() see the cleared TIF_PATCH_PENDING before
>> - * starting the reverse transition.
>> - */
>> + /* Let any remaining calls to klp_update_patch_state() complete */
>> klp_synchronize_transition();
>>
>> - /*
>> - * All patching has stopped, now re-initialize the global variables to
>> - * prepare for the reverse transition.
>> - */
>> - klp_transition_patch->enabled = !klp_transition_patch->enabled;
>> - klp_target_state = !klp_target_state;
>> -
>> - /*
>> - * Enforce the order of the klp_target_state write and the
>> - * TIF_PATCH_PENDING writes in klp_start_transition() to ensure
>> - * klp_update_patch_state() and __klp_sched_try_switch() don't set
>> - * task->patch_state to the wrong value.
>> - */
>> - smp_wmb();
>> -
>> klp_start_transition();
>> }
>>
>> @@ -703,9 +626,9 @@ void klp_copy_process(struct task_struct *child)
>> * the task flag up to date with the parent here.
>> *
>> * The operation is serialized against all klp_*_transition()
>> - * operations by the tasklist_lock. The only exceptions are
>> - * klp_update_patch_state(current) and __klp_sched_try_switch(), but we
>> - * cannot race with them because we are current.
>> + * operations by the tasklist_lock. The only exception is
>> + * klp_update_patch_state(current), but we cannot race with
>> + * that because we are current.
>> */
>> if (test_tsk_thread_flag(current, TIF_PATCH_PENDING))
>> set_tsk_thread_flag(child, TIF_PATCH_PENDING);
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 0e8764d63041..b43fda3c5733 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -8597,7 +8597,6 @@ EXPORT_STATIC_CALL_TRAMP(might_resched);
>> static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
>> int __sched dynamic_cond_resched(void)
>> {
>> - klp_sched_try_switch();
>> if (!static_branch_unlikely(&sk_dynamic_cond_resched))
>> return 0;
>> return __cond_resched();
>> @@ -8746,17 +8745,13 @@ int sched_dynamic_mode(const char *str)
>> #error "Unsupported PREEMPT_DYNAMIC mechanism"
>> #endif
>>
>> -DEFINE_MUTEX(sched_dynamic_mutex);
>> -static bool klp_override;
>> -
>> -static void __sched_dynamic_update(int mode)
>> +void sched_dynamic_update(int mode)
>> {
>> /*
>> * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
>> * the ZERO state, which is invalid.
>> */
>> - if (!klp_override)
>> - preempt_dynamic_enable(cond_resched);
>> + preempt_dynamic_enable(cond_resched);
>> preempt_dynamic_enable(might_resched);
>> preempt_dynamic_enable(preempt_schedule);
>> preempt_dynamic_enable(preempt_schedule_notrace);
>> @@ -8764,79 +8759,36 @@ static void __sched_dynamic_update(int mode)
>>
>> switch (mode) {
>> case preempt_dynamic_none:
>> - if (!klp_override)
>> - preempt_dynamic_enable(cond_resched);
>> + preempt_dynamic_enable(cond_resched);
>> preempt_dynamic_disable(might_resched);
>> preempt_dynamic_disable(preempt_schedule);
>> preempt_dynamic_disable(preempt_schedule_notrace);
>> preempt_dynamic_disable(irqentry_exit_cond_resched);
>> - if (mode != preempt_dynamic_mode)
>> - pr_info("Dynamic Preempt: none\n");
>> + pr_info("Dynamic Preempt: none\n");
>> break;
>>
>> case preempt_dynamic_voluntary:
>> - if (!klp_override)
>> - preempt_dynamic_enable(cond_resched);
>> + preempt_dynamic_enable(cond_resched);
>> preempt_dynamic_enable(might_resched);
>> preempt_dynamic_disable(preempt_schedule);
>> preempt_dynamic_disable(preempt_schedule_notrace);
>> preempt_dynamic_disable(irqentry_exit_cond_resched);
>> - if (mode != preempt_dynamic_mode)
>> - pr_info("Dynamic Preempt: voluntary\n");
>> + pr_info("Dynamic Preempt: voluntary\n");
>> break;
>>
>> case preempt_dynamic_full:
>> - if (!klp_override)
>> - preempt_dynamic_disable(cond_resched);
>> + preempt_dynamic_disable(cond_resched);
>> preempt_dynamic_disable(might_resched);
>> preempt_dynamic_enable(preempt_schedule);
>> preempt_dynamic_enable(preempt_schedule_notrace);
>> preempt_dynamic_enable(irqentry_exit_cond_resched);
>> - if (mode != preempt_dynamic_mode)
>> - pr_info("Dynamic Preempt: full\n");
>> + pr_info("Dynamic Preempt: full\n");
>> break;
>> }
>>
>> preempt_dynamic_mode = mode;
>> }
>>
>> -void sched_dynamic_update(int mode)
>> -{
>> - mutex_lock(&sched_dynamic_mutex);
>> - __sched_dynamic_update(mode);
>> - mutex_unlock(&sched_dynamic_mutex);
>> -}
>> -
>> -#ifdef CONFIG_HAVE_PREEMPT_DYNAMIC_CALL
>> -
>> -static int klp_cond_resched(void)
>> -{
>> - __klp_sched_try_switch();
>> - return __cond_resched();
>> -}
>> -
>> -void sched_dynamic_klp_enable(void)
>> -{
>> - mutex_lock(&sched_dynamic_mutex);
>> -
>> - klp_override = true;
>> - static_call_update(cond_resched, klp_cond_resched);
>> -
>> - mutex_unlock(&sched_dynamic_mutex);
>> -}
>> -
>> -void sched_dynamic_klp_disable(void)
>> -{
>> - mutex_lock(&sched_dynamic_mutex);
>> -
>> - klp_override = false;
>> - __sched_dynamic_update(preempt_dynamic_mode);
>> -
>> - mutex_unlock(&sched_dynamic_mutex);
>> -}
>> -
>> -#endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
>> -
>> static int __init setup_preempt_mode(char *str)
>> {
>> int mode = sched_dynamic_mode(str);
--
ankur
On Tue, Nov 07, 2023 at 06:16:09PM -0500, Steven Rostedt wrote:
> On Tue, 7 Nov 2023 13:56:53 -0800
> Ankur Arora <ankur.a.arora@oracle.com> wrote:
>
> > This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8.
> >
> > Note that removing this commit reintroduces "live patches failing to
> > complete within a reasonable amount of time due to CPU-bound kthreads."
> >
> > Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and
> > existence of cond_resched() so this will need an alternate fix.
We definitely don't want to introduce a regression, something will need
to be figured out before removing cond_resched().
We could hook into preempt_schedule_irq(), but that wouldn't work for
non-ORC.
Another option would be to hook into schedule(). Then livepatch could
set TIF_NEED_RESCHED on remaining unpatched tasks. But again if they go
through the preemption path then we have the same problem for non-ORC.
Worst case we'll need to sprinkle cond_livepatch() everywhere :-/
On Thu, 9 Nov 2023 09:26:37 -0800
Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> On Tue, Nov 07, 2023 at 06:16:09PM -0500, Steven Rostedt wrote:
> > On Tue, 7 Nov 2023 13:56:53 -0800
> > Ankur Arora <ankur.a.arora@oracle.com> wrote:
> >
> > > This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8.
> > >
> > > Note that removing this commit reintroduces "live patches failing to
> > > complete within a reasonable amount of time due to CPU-bound kthreads."
> > >
> > > Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and
> > > existence of cond_resched() so this will need an alternate fix.
>
> We definitely don't want to introduce a regression, something will need
> to be figured out before removing cond_resched().
>
> We could hook into preempt_schedule_irq(), but that wouldn't work for
> non-ORC.
>
> Another option would be to hook into schedule(). Then livepatch could
> set TIF_NEED_RESCHED on remaining unpatched tasks. But again if they go
> through the preemption path then we have the same problem for non-ORC.
>
> Worst case we'll need to sprinkle cond_livepatch() everywhere :-/
>
I guess I'm not fully understanding what the cond rescheds are for. But
would an IPI to all CPUs setting NEED_RESCHED, fix it?
-- Steve
On Thu, Nov 09, 2023 at 12:31:47PM -0500, Steven Rostedt wrote:
> On Thu, 9 Nov 2023 09:26:37 -0800
> Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> > On Tue, Nov 07, 2023 at 06:16:09PM -0500, Steven Rostedt wrote:
> > > On Tue, 7 Nov 2023 13:56:53 -0800
> > > Ankur Arora <ankur.a.arora@oracle.com> wrote:
> > >
> > > > This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8.
> > > >
> > > > Note that removing this commit reintroduces "live patches failing to
> > > > complete within a reasonable amount of time due to CPU-bound kthreads."
> > > >
> > > > Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and
> > > > existence of cond_resched() so this will need an alternate fix.
> >
> > We definitely don't want to introduce a regression, something will need
> > to be figured out before removing cond_resched().
> >
> > We could hook into preempt_schedule_irq(), but that wouldn't work for
> > non-ORC.
> >
> > Another option would be to hook into schedule(). Then livepatch could
> > set TIF_NEED_RESCHED on remaining unpatched tasks. But again if they go
> > through the preemption path then we have the same problem for non-ORC.
> >
> > Worst case we'll need to sprinkle cond_livepatch() everywhere :-/
> >
>
> I guess I'm not fully understanding what the cond rescheds are for. But
> would an IPI to all CPUs setting NEED_RESCHED, fix it?
If all livepatch arches had the ORC unwinder, yes.
The problem is that frame pointer (and similar) unwinders can't reliably
unwind past an interrupt frame.
Josh Poimboeuf <jpoimboe@kernel.org> writes:
> On Thu, Nov 09, 2023 at 12:31:47PM -0500, Steven Rostedt wrote:
>> On Thu, 9 Nov 2023 09:26:37 -0800
>> Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>>
>> > On Tue, Nov 07, 2023 at 06:16:09PM -0500, Steven Rostedt wrote:
>> > > On Tue, 7 Nov 2023 13:56:53 -0800
>> > > Ankur Arora <ankur.a.arora@oracle.com> wrote:
>> > >
>> > > > This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8.
>> > > >
>> > > > Note that removing this commit reintroduces "live patches failing to
>> > > > complete within a reasonable amount of time due to CPU-bound kthreads."
>> > > >
>> > > > Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and
>> > > > existence of cond_resched() so this will need an alternate fix.
>> >
>> > We definitely don't want to introduce a regression, something will need
>> > to be figured out before removing cond_resched().
>> >
>> > We could hook into preempt_schedule_irq(), but that wouldn't work for
>> > non-ORC.
>> >
>> > Another option would be to hook into schedule(). Then livepatch could
>> > set TIF_NEED_RESCHED on remaining unpatched tasks. But again if they go
>> > through the preemption path then we have the same problem for non-ORC.
>> >
>> > Worst case we'll need to sprinkle cond_livepatch() everywhere :-/
>> >
>>
>> I guess I'm not fully understanding what the cond rescheds are for. But
>> would an IPI to all CPUs setting NEED_RESCHED, fix it?
Yeah. We could just temporarily toggle to full preemption, when
NEED_RESCHED_LAZY is always upgraded to NEED_RESCHED which will
then send IPIs.
> If all livepatch arches had the ORC unwinder, yes.
>
> The problem is that frame pointer (and similar) unwinders can't reliably
> unwind past an interrupt frame.
Ah, I wonder if we could just disable the preempt_schedule_irq() path
temporarily? Hooking into schedule() alongside something like this:
@@ -379,7 +379,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
void irqentry_exit_cond_resched(void)
{
- if (!preempt_count()) {
+ if (klp_cond_resched_disable() && !preempt_count()) {
The problem would be tasks that don't go through any preemptible
sections.
--
ankur
On Thu, Nov 09, 2023 at 02:50:48PM -0800, Ankur Arora wrote:
> >> I guess I'm not fully understanding what the cond rescheds are for. But
> >> would an IPI to all CPUs setting NEED_RESCHED, fix it?
>
> Yeah. We could just temporarily toggle to full preemption, when
> NEED_RESCHED_LAZY is always upgraded to NEED_RESCHED which will
> then send IPIs.
>
> > If all livepatch arches had the ORC unwinder, yes.
> >
> > The problem is that frame pointer (and similar) unwinders can't reliably
> > unwind past an interrupt frame.
>
> Ah, I wonder if we could just disable the preempt_schedule_irq() path
> temporarily? Hooking into schedule() alongside something like this:
>
> @@ -379,7 +379,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
>
> void irqentry_exit_cond_resched(void)
> {
> - if (!preempt_count()) {
> + if (klp_cond_resched_disable() && !preempt_count()) {
>
> The problem would be tasks that don't go through any preemptible
> sections.
Let me back up a bit and explain what klp is trying to do.
When a livepatch is applied, klp needs to unwind all the tasks,
preferably within a reasonable amount of time.
We can't unwind task A from task B while task A is running, since task A
could be changing the stack during the unwind. So task A needs to be
blocked or asleep. The only exception to that is if the unwind happens
in the context of task A itself.
The problem we were seeing was CPU-bound kthreads (e.g., vhost_worker)
not getting patched within a reasonable amount of time. We fixed it by
hooking the klp unwind into cond_resched() so it can unwind from the
task itself.
It only worked because we had a non-preempted hook (because non-ORC
unwinders can't unwind reliably through preemption) which called klp to
unwind from the context of the task.
Without something to hook into, we have a problem. We could of course
hook into schedule(), but if the kthread never calls schedule() from a
non-preempted context then it still doesn't help.
Josh Poimboeuf <jpoimboe@kernel.org> writes:
> On Thu, Nov 09, 2023 at 02:50:48PM -0800, Ankur Arora wrote:
>> >> I guess I'm not fully understanding what the cond rescheds are for. But
>> >> would an IPI to all CPUs setting NEED_RESCHED, fix it?
>>
>> Yeah. We could just temporarily toggle to full preemption, when
>> NEED_RESCHED_LAZY is always upgraded to NEED_RESCHED which will
>> then send IPIs.
>>
>> > If all livepatch arches had the ORC unwinder, yes.
>> >
>> > The problem is that frame pointer (and similar) unwinders can't reliably
>> > unwind past an interrupt frame.
>>
>> Ah, I wonder if we could just disable the preempt_schedule_irq() path
>> temporarily? Hooking into schedule() alongside something like this:
>>
>> @@ -379,7 +379,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
>>
>> void irqentry_exit_cond_resched(void)
>> {
>> - if (!preempt_count()) {
>> + if (klp_cond_resched_disable() && !preempt_count()) {
>>
>> The problem would be tasks that don't go through any preemptible
>> sections.
>
> Let me back up a bit and explain what klp is trying to do.
>
> When a livepatch is applied, klp needs to unwind all the tasks,
> preferably within a reasonable amount of time.
>
> We can't unwind task A from task B while task A is running, since task A
> could be changing the stack during the unwind. So task A needs to be
> blocked or asleep. The only exception to that is if the unwind happens
> in the context of task A itself.
> The problem we were seeing was CPU-bound kthreads (e.g., vhost_worker)
> not getting patched within a reasonable amount of time. We fixed it by
> hooking the klp unwind into cond_resched() so it can unwind from the
> task itself.
Right, so the task calls schedule() itself via cond_resched() and that
works. If the task schedules out by calling preempt_enable() that
presumably works as well.
So, that leaves two paths where we can't unwind:
1. a task never entering or leaving preemptible sections
2. or, a task which gets preempted in irqentry_exit_cond_resched()
This we could disable temporarily.
> It only worked because we had a non-preempted hook (because non-ORC
> unwinders can't unwind reliably through preemption) which called klp to
> unwind from the context of the task.
>
> Without something to hook into, we have a problem. We could of course
> hook into schedule(), but if the kthread never calls schedule() from a
> non-preempted context then it still doesn't help.
Yeah agreed. The first one is a problem. And, that's a problem with the
removal of cond_resched() generally. Because the way to fix case 1 was
typically to add a cond_resched() when softlockups were seen or in
code review.
--
ankur
On Thu, 9 Nov 2023 09:51:18 -0800
Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> > I guess I'm not fully understanding what the cond rescheds are for. But
> > would an IPI to all CPUs setting NEED_RESCHED, fix it?
>
> If all livepatch arches had the ORC unwinder, yes.
>
> The problem is that frame pointer (and similar) unwinders can't reliably
> unwind past an interrupt frame.
Perhaps we can use this to push those archs with bad unwinders to port over
ORC unwinding ;-)
-- Steve
@@ -13,7 +13,6 @@
#include <linux/ftrace.h>
#include <linux/completion.h>
#include <linux/list.h>
-#include <linux/livepatch_sched.h>
#if IS_ENABLED(CONFIG_LIVEPATCH)
deleted file mode 100644
@@ -1,29 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-#ifndef _LINUX_LIVEPATCH_SCHED_H_
-#define _LINUX_LIVEPATCH_SCHED_H_
-
-#include <linux/jump_label.h>
-#include <linux/static_call_types.h>
-
-#ifdef CONFIG_LIVEPATCH
-
-void __klp_sched_try_switch(void);
-
-#if !defined(CONFIG_PREEMPT_DYNAMIC) || !defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
-DECLARE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
-
-static __always_inline void klp_sched_try_switch(void)
-{
- if (static_branch_unlikely(&klp_sched_try_switch_key))
- __klp_sched_try_switch();
-}
-
-#endif /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
-#else /* !CONFIG_LIVEPATCH */
-static inline void klp_sched_try_switch(void) {}
-static inline void __klp_sched_try_switch(void) {}
-#endif /* CONFIG_LIVEPATCH */
-
-#endif /* _LINUX_LIVEPATCH_SCHED_H_ */
@@ -36,7 +36,6 @@
#include <linux/seqlock.h>
#include <linux/kcsan.h>
#include <linux/rv.h>
-#include <linux/livepatch_sched.h>
#include <asm/kmap_size.h>
/* task_struct member predeclarations (sorted alphabetically): */
@@ -2087,9 +2086,6 @@ extern int __cond_resched(void);
#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-void sched_dynamic_klp_enable(void);
-void sched_dynamic_klp_disable(void);
-
DECLARE_STATIC_CALL(cond_resched, __cond_resched);
static __always_inline int _cond_resched(void)
@@ -2098,7 +2094,6 @@ static __always_inline int _cond_resched(void)
}
#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
-
extern int dynamic_cond_resched(void);
static __always_inline int _cond_resched(void)
@@ -2106,25 +2101,20 @@ static __always_inline int _cond_resched(void)
return dynamic_cond_resched();
}
-#else /* !CONFIG_PREEMPTION */
+#else
static inline int _cond_resched(void)
{
- klp_sched_try_switch();
return __cond_resched();
}
-#endif /* PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
+#endif /* CONFIG_PREEMPT_DYNAMIC */
-#else /* CONFIG_PREEMPTION && !CONFIG_PREEMPT_DYNAMIC */
+#else
-static inline int _cond_resched(void)
-{
- klp_sched_try_switch();
- return 0;
-}
+static inline int _cond_resched(void) { return 0; }
-#endif /* !CONFIG_PREEMPTION || CONFIG_PREEMPT_DYNAMIC */
+#endif /* !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) */
#define cond_resched() ({ \
__might_resched(__FILE__, __LINE__, 0); \
@@ -33,7 +33,6 @@
*
* - klp_ftrace_handler()
* - klp_update_patch_state()
- * - __klp_sched_try_switch()
*/
DEFINE_MUTEX(klp_mutex);
@@ -9,7 +9,6 @@
#include <linux/cpu.h>
#include <linux/stacktrace.h>
-#include <linux/static_call.h>
#include "core.h"
#include "patch.h"
#include "transition.h"
@@ -27,25 +26,6 @@ static int klp_target_state = KLP_UNDEFINED;
static unsigned int klp_signals_cnt;
-/*
- * When a livepatch is in progress, enable klp stack checking in
- * cond_resched(). This helps CPU-bound kthreads get patched.
- */
-#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
-#define klp_cond_resched_enable() sched_dynamic_klp_enable()
-#define klp_cond_resched_disable() sched_dynamic_klp_disable()
-
-#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
-DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
-EXPORT_SYMBOL(klp_sched_try_switch_key);
-
-#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
-#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
-
-#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
/*
* This work can be performed periodically to finish patching or unpatching any
* "straggler" tasks which failed to transition in the first attempt.
@@ -194,8 +174,8 @@ void klp_update_patch_state(struct task_struct *task)
* barrier (smp_rmb) for two cases:
*
* 1) Enforce the order of the TIF_PATCH_PENDING read and the
- * klp_target_state read. The corresponding write barriers are in
- * klp_init_transition() and klp_reverse_transition().
+ * klp_target_state read. The corresponding write barrier is in
+ * klp_init_transition().
*
* 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
* of func->transition, if klp_ftrace_handler() is called later on
@@ -363,44 +343,6 @@ static bool klp_try_switch_task(struct task_struct *task)
return !ret;
}
-void __klp_sched_try_switch(void)
-{
- if (likely(!klp_patch_pending(current)))
- return;
-
- /*
- * This function is called from cond_resched() which is called in many
- * places throughout the kernel. Using the klp_mutex here might
- * deadlock.
- *
- * Instead, disable preemption to prevent racing with other callers of
- * klp_try_switch_task(). Thanks to task_call_func() they won't be
- * able to switch this task while it's running.
- */
- preempt_disable();
-
- /*
- * Make sure current didn't get patched between the above check and
- * preempt_disable().
- */
- if (unlikely(!klp_patch_pending(current)))
- goto out;
-
- /*
- * Enforce the order of the TIF_PATCH_PENDING read above and the
- * klp_target_state read in klp_try_switch_task(). The corresponding
- * write barriers are in klp_init_transition() and
- * klp_reverse_transition().
- */
- smp_rmb();
-
- klp_try_switch_task(current);
-
-out:
- preempt_enable();
-}
-EXPORT_SYMBOL(__klp_sched_try_switch);
-
/*
* Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
* Kthreads with TIF_PATCH_PENDING set are woken up.
@@ -507,8 +449,7 @@ void klp_try_complete_transition(void)
return;
}
- /* Done! Now cleanup the data structures. */
- klp_cond_resched_disable();
+ /* we're done, now cleanup the data structures */
patch = klp_transition_patch;
klp_complete_transition();
@@ -560,8 +501,6 @@ void klp_start_transition(void)
set_tsk_thread_flag(task, TIF_PATCH_PENDING);
}
- klp_cond_resched_enable();
-
klp_signals_cnt = 0;
}
@@ -617,9 +556,8 @@ void klp_init_transition(struct klp_patch *patch, int state)
* see a func in transition with a task->patch_state of KLP_UNDEFINED.
*
* Also enforce the order of the klp_target_state write and future
- * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() and
- * __klp_sched_try_switch() don't set a task->patch_state to
- * KLP_UNDEFINED.
+ * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
+ * set a task->patch_state to KLP_UNDEFINED.
*/
smp_wmb();
@@ -655,10 +593,14 @@ void klp_reverse_transition(void)
klp_target_state == KLP_PATCHED ? "patching to unpatching" :
"unpatching to patching");
+ klp_transition_patch->enabled = !klp_transition_patch->enabled;
+
+ klp_target_state = !klp_target_state;
+
/*
* Clear all TIF_PATCH_PENDING flags to prevent races caused by
- * klp_update_patch_state() or __klp_sched_try_switch() running in
- * parallel with the reverse transition.
+ * klp_update_patch_state() running in parallel with
+ * klp_start_transition().
*/
read_lock(&tasklist_lock);
for_each_process_thread(g, task)
@@ -668,28 +610,9 @@ void klp_reverse_transition(void)
for_each_possible_cpu(cpu)
clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
- /*
- * Make sure all existing invocations of klp_update_patch_state() and
- * __klp_sched_try_switch() see the cleared TIF_PATCH_PENDING before
- * starting the reverse transition.
- */
+ /* Let any remaining calls to klp_update_patch_state() complete */
klp_synchronize_transition();
- /*
- * All patching has stopped, now re-initialize the global variables to
- * prepare for the reverse transition.
- */
- klp_transition_patch->enabled = !klp_transition_patch->enabled;
- klp_target_state = !klp_target_state;
-
- /*
- * Enforce the order of the klp_target_state write and the
- * TIF_PATCH_PENDING writes in klp_start_transition() to ensure
- * klp_update_patch_state() and __klp_sched_try_switch() don't set
- * task->patch_state to the wrong value.
- */
- smp_wmb();
-
klp_start_transition();
}
@@ -703,9 +626,9 @@ void klp_copy_process(struct task_struct *child)
* the task flag up to date with the parent here.
*
* The operation is serialized against all klp_*_transition()
- * operations by the tasklist_lock. The only exceptions are
- * klp_update_patch_state(current) and __klp_sched_try_switch(), but we
- * cannot race with them because we are current.
+ * operations by the tasklist_lock. The only exception is
+ * klp_update_patch_state(current), but we cannot race with
+ * that because we are current.
*/
if (test_tsk_thread_flag(current, TIF_PATCH_PENDING))
set_tsk_thread_flag(child, TIF_PATCH_PENDING);
@@ -8597,7 +8597,6 @@ EXPORT_STATIC_CALL_TRAMP(might_resched);
static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
int __sched dynamic_cond_resched(void)
{
- klp_sched_try_switch();
if (!static_branch_unlikely(&sk_dynamic_cond_resched))
return 0;
return __cond_resched();
@@ -8746,17 +8745,13 @@ int sched_dynamic_mode(const char *str)
#error "Unsupported PREEMPT_DYNAMIC mechanism"
#endif
-DEFINE_MUTEX(sched_dynamic_mutex);
-static bool klp_override;
-
-static void __sched_dynamic_update(int mode)
+void sched_dynamic_update(int mode)
{
/*
* Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
* the ZERO state, which is invalid.
*/
- if (!klp_override)
- preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(cond_resched);
preempt_dynamic_enable(might_resched);
preempt_dynamic_enable(preempt_schedule);
preempt_dynamic_enable(preempt_schedule_notrace);
@@ -8764,79 +8759,36 @@ static void __sched_dynamic_update(int mode)
switch (mode) {
case preempt_dynamic_none:
- if (!klp_override)
- preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(cond_resched);
preempt_dynamic_disable(might_resched);
preempt_dynamic_disable(preempt_schedule);
preempt_dynamic_disable(preempt_schedule_notrace);
preempt_dynamic_disable(irqentry_exit_cond_resched);
- if (mode != preempt_dynamic_mode)
- pr_info("Dynamic Preempt: none\n");
+ pr_info("Dynamic Preempt: none\n");
break;
case preempt_dynamic_voluntary:
- if (!klp_override)
- preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(cond_resched);
preempt_dynamic_enable(might_resched);
preempt_dynamic_disable(preempt_schedule);
preempt_dynamic_disable(preempt_schedule_notrace);
preempt_dynamic_disable(irqentry_exit_cond_resched);
- if (mode != preempt_dynamic_mode)
- pr_info("Dynamic Preempt: voluntary\n");
+ pr_info("Dynamic Preempt: voluntary\n");
break;
case preempt_dynamic_full:
- if (!klp_override)
- preempt_dynamic_disable(cond_resched);
+ preempt_dynamic_disable(cond_resched);
preempt_dynamic_disable(might_resched);
preempt_dynamic_enable(preempt_schedule);
preempt_dynamic_enable(preempt_schedule_notrace);
preempt_dynamic_enable(irqentry_exit_cond_resched);
- if (mode != preempt_dynamic_mode)
- pr_info("Dynamic Preempt: full\n");
+ pr_info("Dynamic Preempt: full\n");
break;
}
preempt_dynamic_mode = mode;
}
-void sched_dynamic_update(int mode)
-{
- mutex_lock(&sched_dynamic_mutex);
- __sched_dynamic_update(mode);
- mutex_unlock(&sched_dynamic_mutex);
-}
-
-#ifdef CONFIG_HAVE_PREEMPT_DYNAMIC_CALL
-
-static int klp_cond_resched(void)
-{
- __klp_sched_try_switch();
- return __cond_resched();
-}
-
-void sched_dynamic_klp_enable(void)
-{
- mutex_lock(&sched_dynamic_mutex);
-
- klp_override = true;
- static_call_update(cond_resched, klp_cond_resched);
-
- mutex_unlock(&sched_dynamic_mutex);
-}
-
-void sched_dynamic_klp_disable(void)
-{
- mutex_lock(&sched_dynamic_mutex);
-
- klp_override = false;
- __sched_dynamic_update(preempt_dynamic_mode);
-
- mutex_unlock(&sched_dynamic_mutex);
-}
-
-#endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
static int __init setup_preempt_mode(char *str)
{
int mode = sched_dynamic_mode(str);