Messages in this thread Patch in this message |  | | From | Frederic Weisbecker <> | Subject | [PATCH 1/6] posix-cpu-timers: Assert task sighand is locked while starting cputime counter | Date | Mon, 26 Jul 2021 14:55:08 +0200 |
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Starting the process wide cputime counter needs to be done in the same sighand locking sequence than actually arming the related timer otherwise we risk races against concurrent timers setting/expiring in the same threadgroup.
Detecting that we start the cputime counter without holding the sighand lock is a first step toward debugging such situations.
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Eric W. Biederman <ebiederm@xmission.com> --- include/linux/sched/signal.h | 6 ++++++ kernel/signal.c | 15 +++++++++++++++ kernel/time/posix-cpu-timers.c | 2 ++ 3 files changed, 23 insertions(+)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index b9126fe06c3f..0310a5add9ab 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -714,6 +714,12 @@ static inline void unlock_task_sighand(struct task_struct *task, spin_unlock_irqrestore(&task->sighand->siglock, *flags); } +#ifdef CONFIG_LOCKDEP +extern void lockdep_assert_task_sighand_held(struct task_struct *task); +#else +static inline void lockdep_assert_task_sighand_held(struct task_struct *task) { } +#endif + static inline unsigned long task_rlimit(const struct task_struct *task, unsigned int limit) { diff --git a/kernel/signal.c b/kernel/signal.c index a3229add4455..52b6abec0ff8 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1413,6 +1413,21 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk, return sighand; } +#ifdef CONFIG_LOCKDEP +void lockdep_assert_task_sighand_held(struct task_struct *task) +{ + struct sighand_struct *sighand; + + rcu_read_lock(); + sighand = rcu_dereference(task->sighand); + if (sighand) + lockdep_assert_held(&sighand->siglock); + else + WARN_ON_ONCE(1); + rcu_read_unlock(); +} +#endif + /* * send signal info to all the members of a group */ diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 517be7fd175e..4693d3c71e7e 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -291,6 +291,8 @@ static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples) struct thread_group_cputimer *cputimer = &tsk->signal->cputimer; struct posix_cputimers *pct = &tsk->signal->posix_cputimers; + lockdep_assert_task_sighand_held(tsk); + /* Check if cputimer isn't running. This is accessed without locking. */ if (!READ_ONCE(pct->timers_active)) { struct task_cputime sum; -- 2.25.1
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