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Biederman" , Andy Lutomirski , Sebastian Andrzej Siewior , Peter Zijlstra , "Liam R. Howlett" , Fenghua Yu , Andrei Vagin , linux-kernel@vger.kernel.org (open list) Cc: Wander Lairson Costa , Hu Chunyu , Oleg Nesterov , Valentin Schneider , Paul McKenney Subject: [PATCH v3] kernel/fork: beware of __put_task_struct calling context Date: Wed, 1 Feb 2023 09:45:40 -0300 Message-Id: <20230201124541.62104-1-wander@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1756634502171563246?= X-GMAIL-MSGID: =?utf-8?q?1756634502171563246?= Under PREEMPT_RT, __put_task_struct() indirectly acquires sleeping locks. Therefore, it can't be called from an non-preemptible context. One practical example is splat inside inactive_task_timer(), which is called in a interrupt context: CPU: 1 PID: 2848 Comm: life Kdump: loaded Tainted: G W --------- Hardware name: HP ProLiant DL388p Gen8, BIOS P70 07/15/2012 Call Trace: dump_stack_lvl+0x57/0x7d mark_lock_irq.cold+0x33/0xba ? stack_trace_save+0x4b/0x70 ? save_trace+0x55/0x150 mark_lock+0x1e7/0x400 mark_usage+0x11d/0x140 __lock_acquire+0x30d/0x930 lock_acquire.part.0+0x9c/0x210 ? refill_obj_stock+0x3d/0x3a0 ? rcu_read_lock_sched_held+0x3f/0x70 ? trace_lock_acquire+0x38/0x140 ? lock_acquire+0x30/0x80 ? refill_obj_stock+0x3d/0x3a0 rt_spin_lock+0x27/0xe0 ? refill_obj_stock+0x3d/0x3a0 refill_obj_stock+0x3d/0x3a0 ? inactive_task_timer+0x1ad/0x340 kmem_cache_free+0x357/0x560 inactive_task_timer+0x1ad/0x340 ? switched_from_dl+0x2d0/0x2d0 __run_hrtimer+0x8a/0x1a0 __hrtimer_run_queues+0x91/0x130 hrtimer_interrupt+0x10f/0x220 __sysvec_apic_timer_interrupt+0x7b/0xd0 sysvec_apic_timer_interrupt+0x4f/0xd0 ? asm_sysvec_apic_timer_interrupt+0xa/0x20 asm_sysvec_apic_timer_interrupt+0x12/0x20 RIP: 0033:0x7fff196bf6f5 Instead of calling __put_task_struct() directly, we defer it using call_rcu(). A more natural approach would use a workqueue, but since in PREEMPT_RT, we can't allocate dynamic memory from atomic context, the code would become more complex because we would need to put the work_struct instance in the task_struct and initialize it when we allocate a new task_struct. Signed-off-by: Wander Lairson Costa Reported-by: Hu Chunyu Suggested-by: Oleg Nesterov Suggested-by: Valentin Schneider Cc: Paul McKenney --- kernel/fork.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index 9f7fe3541897..b2d0d62c9b9d 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -840,7 +840,7 @@ static inline void put_signal_struct(struct signal_struct *sig) free_signal_struct(sig); } -void __put_task_struct(struct task_struct *tsk) +static void ___put_task_struct(struct task_struct *tsk) { WARN_ON(!tsk->exit_state); WARN_ON(refcount_read(&tsk->usage)); @@ -857,6 +857,26 @@ void __put_task_struct(struct task_struct *tsk) sched_core_free(tsk); free_task(tsk); } + +static void __delayed_put_task_struct(struct rcu_head *rhp) +{ + struct task_struct *task = container_of(rhp, struct task_struct, rcu); + + ___put_task_struct(task); +} + +void __put_task_struct(struct task_struct *tsk) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && (!preemptible() || !in_task())) + /* + * under PREEMPT_RT, we can't call put_task_struct + * in atomic context because it will indirectly + * acquire sleeping locks. + */ + call_rcu(&tsk->rcu, __delayed_put_task_struct); + else + ___put_task_struct(tsk); +} EXPORT_SYMBOL_GPL(__put_task_struct); void __init __weak arch_task_cache_init(void) { }