linux-kernel - Re: [PATCH v4] sched: do not call __put_task_struct() on rt if pi_blocked

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <ucooiludwnen2gxm6pjypzloif23w4t37vrpml75egpkifbc4z@tmrs462ju7om>
Date: Tue, 22 Apr 2025 12:50:06 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Clark Williams <clrkwllms@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, Tejun Heo <tj@...nel.org>, 
	David Vernet <dvernet@...a.com>, Barret Rhoden <brho@...gle.com>, Josh Don <joshdon@...gle.com>, 
	Crystal Wood <crwood@...hat.com>, linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, 
	Juri Lelli <juri.lelli@...hat.com>, Ben Segall <bsegall@...gle.com>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Ingo Molnar <mingo@...hat.com>, Mel Gorman <mgorman@...e.de>, 
	Peter Zijlstra <peterz@...radead.org>, Valentin Schneider <vschneid@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, lclaudio00@...il.com
Subject: Re: [PATCH v4] sched: do not call __put_task_struct() on rt if
 pi_blocked_on is set

On Thu, Apr 10, 2025 at 03:19:28PM -0300, Luis Claudio R. Goncalves wrote:
> With PREEMPT_RT enabled, some of the calls to put_task_struct() coming
> from rt_mutex_adjust_prio_chain() could happen in preemptible context and
> with a mutex enqueued. That could lead to this sequence:
> 
>         rt_mutex_adjust_prio_chain()
>           put_task_struct()
>             __put_task_struct()
>               sched_ext_free()
>                 spin_lock_irqsave()
>                   rtlock_lock() --->  TRIGGERS
>                                       lockdep_assert(!current->pi_blocked_on);
> 
> Fix that by unconditionally resorting to the deferred call to
> __put_task_struct() if PREEMPT_RT is enabled.
> 
> Suggested-by: Crystal Wood <crwood@...hat.com>
> Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@...hat.com>
> ---
> 
> v2: (Rostedt) remove the #ifdef from put_task_struct() and create
>     tsk_is_pi_blocked_on() in sched.h to make the change cleaner.
> v3: (Sebastian, PeterZ) always call the deferred __put_task_struct() on RT.
> v4: Fix the implementation of what was requested on v3.
> 
>  include/linux/sched/task.h |   17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
> index 0f2aeb37bbb04..51678a541477a 100644
> --- a/include/linux/sched/task.h
> +++ b/include/linux/sched/task.h
> @@ -134,11 +134,8 @@ static inline void put_task_struct(struct task_struct *t)
>  	if (!refcount_dec_and_test(&t->usage))
>  		return;
>  
> -	/*
> -	 * In !RT, it is always safe to call __put_task_struct().
> -	 * Under RT, we can only call it in preemptible context.
> -	 */
> -	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible()) {
> +	/* In !RT, it is always safe to call __put_task_struct(). */
> +	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
>  		static DEFINE_WAIT_OVERRIDE_MAP(put_task_map, LD_WAIT_SLEEP);
>  
>  		lock_map_acquire_try(&put_task_map);
> @@ -148,11 +145,13 @@ static inline void put_task_struct(struct task_struct *t)
>  	}
>  
>  	/*
> -	 * under PREEMPT_RT, we can't call put_task_struct
> +	 * Under PREEMPT_RT, we can't call __put_task_struct
>  	 * in atomic context because it will indirectly
> -	 * acquire sleeping locks.
> +	 * acquire sleeping locks. The same is true if the
> +	 * current process has a mutex enqueued (blocked on
> +	 * a PI chain).
>  	 *
> -	 * call_rcu() will schedule delayed_put_task_struct_rcu()
> +	 * call_rcu() will schedule __put_task_struct_rcu_cb()
>  	 * to be called in process context.
>  	 *
>  	 * __put_task_struct() is called when
> @@ -165,7 +164,7 @@ static inline void put_task_struct(struct task_struct *t)
>  	 *
>  	 * delayed_free_task() also uses ->rcu, but it is only called
>  	 * when it fails to fork a process. Therefore, there is no
> -	 * way it can conflict with put_task_struct().
> +	 * way it can conflict with __put_task_struct().
>  	 */
>  	call_rcu(&t->rcu, __put_task_struct_rcu_cb);
>  }
> 

Reviewed-by: Wander Lairson Costa <wander@...hat.com>