[v3] Crash: add lock to serialize crash hotplug handling
Commit Message
Eric reported that handling corresponding crash hotplug event can be
failed easily when many memory hotplug event are notified in a short
period. They failed because failing to take __kexec_lock.
=======
[ 78.714569] Fallback order for Node 0: 0
[ 78.714575] Built 1 zonelists, mobility grouping on. Total pages: 1817886
[ 78.717133] Policy zone: Normal
[ 78.724423] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
[ 78.727207] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
[ 80.056643] PEFILE: Unsigned PE binary
=======
The memory hotplug events are notified very quickly and very many,
while the handling of crash hotplug is much slower relatively. So the
atomic variable __kexec_lock and kexec_trylock() can't guarantee the
serialization of crash hotplug handling.
Here, add a new mutex lock __crash_hotplug_lock to serialize crash
hotplug handling specifically. This doesn't impact the usage of
__kexec_lock.
Signed-off-by: Baoquan He <bhe@redhat.com>
---
v2->v3:
- crash_check_update_elfcorehdr() need take __crash_hotplug_lock
too because there's tiny racing window when kexec_load interface
is taken. Eric pointed out this.
v1->v2:
- Move mutex lock definition into CONFIG_CRASH_HOTPLUG ifdeffery
scope in kernel/crash_core.c because the lock is only needed and
used in that scope. Suggested by Eric.
kernel/crash_core.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
Comments
On Tue, 26 Sep 2023 20:09:05 +0800 Baoquan He <bhe@redhat.com> wrote:
> Eric reported that handling corresponding crash hotplug event can be
> failed easily when many memory hotplug event are notified in a short
> period. They failed because failing to take __kexec_lock.
I'm assuming that this failure is sufficiently likely so as to justify a -stable
backport of the fix. Please let me know if this is incorrect.
On 9/26/23 15:50, Andrew Morton wrote:
> On Tue, 26 Sep 2023 20:09:05 +0800 Baoquan He <bhe@redhat.com> wrote:
>
>> Eric reported that handling corresponding crash hotplug event can be
>> failed easily when many memory hotplug event are notified in a short
>> period. They failed because failing to take __kexec_lock.
>
> I'm assuming that this failure is sufficiently likely so as to justify a -stable
> backport of the fix. Please let me know if this is incorrect.
Andrew,
Correct, this is sufficiently likely to happen.
Thanks,
eric
On 09/26/23 at 04:53pm, Eric DeVolder wrote:
>
>
> On 9/26/23 15:50, Andrew Morton wrote:
> > On Tue, 26 Sep 2023 20:09:05 +0800 Baoquan He <bhe@redhat.com> wrote:
> >
> > > Eric reported that handling corresponding crash hotplug event can be
> > > failed easily when many memory hotplug event are notified in a short
> > > period. They failed because failing to take __kexec_lock.
> >
> > I'm assuming that this failure is sufficiently likely so as to justify a -stable
> > backport of the fix. Please let me know if this is incorrect.
>
> Andrew,
> Correct, this is sufficiently likely to happen.
Agree. Maybe a Fixes tag need be added:
===
Fixes: 247262756121 ("crash: add generic infrastructure for crash hotplug support")
On 26/09/23 20:09, Baoquan He wrote:
> Eric reported that handling corresponding crash hotplug event can be
> failed easily when many memory hotplug event are notified in a short
> period. They failed because failing to take __kexec_lock.
>
> =======
> [ 78.714569] Fallback order for Node 0: 0
> [ 78.714575] Built 1 zonelists, mobility grouping on. Total pages: 1817886
> [ 78.717133] Policy zone: Normal
> [ 78.724423] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
> [ 78.727207] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
> [ 80.056643] PEFILE: Unsigned PE binary
> =======
>
> The memory hotplug events are notified very quickly and very many,
> while the handling of crash hotplug is much slower relatively. So the
> atomic variable __kexec_lock and kexec_trylock() can't guarantee the
> serialization of crash hotplug handling.
>
> Here, add a new mutex lock __crash_hotplug_lock to serialize crash
> hotplug handling specifically. This doesn't impact the usage of
> __kexec_lock.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
@@ -739,6 +739,17 @@ subsys_initcall(crash_notes_memory_init);
#undef pr_fmt
#define pr_fmt(fmt) "crash hp: " fmt
+/*
+ * Different than kexec/kdump loading/unloading/jumping/shrinking which
+ * usually rarely happen, there will be many crash hotplug events notified
+ * during one short period, e.g one memory board is hot added and memory
+ * regions are online. So mutex lock __crash_hotplug_lock is used to
+ * serialize the crash hotplug handling specifically.
+ */
+DEFINE_MUTEX(__crash_hotplug_lock);
+#define crash_hotplug_lock() mutex_lock(&__crash_hotplug_lock)
+#define crash_hotplug_unlock() mutex_unlock(&__crash_hotplug_lock)
+
/*
* This routine utilized when the crash_hotplug sysfs node is read.
* It reflects the kernel's ability/permission to update the crash
@@ -748,9 +759,11 @@ int crash_check_update_elfcorehdr(void)
{
int rc = 0;
+ crash_hotplug_lock();
/* Obtain lock while reading crash information */
if (!kexec_trylock()) {
pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
+ crash_hotplug_unlock();
return 0;
}
if (kexec_crash_image) {
@@ -761,6 +774,7 @@ int crash_check_update_elfcorehdr(void)
}
/* Release lock now that update complete */
kexec_unlock();
+ crash_hotplug_unlock();
return rc;
}
@@ -783,9 +797,11 @@ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
{
struct kimage *image;
+ crash_hotplug_lock();
/* Obtain lock while changing crash information */
if (!kexec_trylock()) {
pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
+ crash_hotplug_unlock();
return;
}
@@ -852,6 +868,7 @@ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
out:
/* Release lock now that update complete */
kexec_unlock();
+ crash_hotplug_unlock();
}
static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)