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posix-cpu-timers: Prevent enqueueing when PF_EXITING is set

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To prepare for cleaning up POSIX CPU timers in do_exit(), prevent
enqueueing POSIX CPU timers on a task which has PF_EXITING set.  Queueing a
timer on such a task is pointless because the task won't expire the timer
anymore.

The same applies to process wide timers when tsk::signal::flags has
SIGNAL_GROUP_EXIT set.

Pretending that the timer is armed allows to keep the POSIX timer mechanism
"working" so that the timer stays accessible up to the point where a task
is unhashed.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Kijo Park <red993688@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://patch.msgid.link/20260911090541.892445443@kernel.org
This commit is contained in:
Thomas Gleixner 2026-09-11 11:09:40 +02:00
parent 760ad335d6
commit 54ad1e0ea4
1 changed files with 28 additions and 0 deletions
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28
kernel/time/posix-cpu-timers.c
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@ -628,6 +628,7 @@ static int posix_cpu_timer_del(struct k_itimer *timer)
}
if (!ret) {
WARN_ON_ONCE(cpu_timer_queued(&timer->it.cpu));
put_pid(timer->it.cpu.pid);
timer->it_status = POSIX_TIMER_DISARMED;
}
@ -674,6 +675,27 @@ void posix_cpu_timers_exit_group(struct task_struct *tsk)
cleanup_timers(&tsk->signal->posix_cputimers);
}
/*
* This function validates that POSIX CPU timers can be safely enqueued on the
* target task.
*
* Enqueue is allowed when PF_EXITING is not set. If set then it is only allowed
* for process shared timers (type = PIDTYPE_TGID) as long as tsk::signal::flags
* does not have SIGNAL_GROUP_EXIT set. PIDTYPE_PID targets are not allowed at
* all when the task has PF_EXITING set.
*
* This guarantees that after the POSIX timer cleanup in posixtimer_exit() no
* POSIX CPU timers are queued on the task or in case of a group exit on the
* process.
*/
static inline bool task_can_enqueue_timer(struct task_struct *tsk, enum pid_type type)
{
if (likely(!(tsk->flags & PF_EXITING)))
return true;
return type == PIDTYPE_TGID && !(tsk->signal->flags & SIGNAL_GROUP_EXIT);
}
/*
* Insert the timer on the appropriate list before any timers that
* expire later. This must be called with the sighand lock held.
@ -684,7 +706,13 @@ static void arm_timer(struct k_itimer *timer, struct task_struct *p)
struct cpu_timer *ctmr = &timer->it.cpu;
u64 newexp = cpu_timer_getexpires(ctmr);
lockdep_assert_held(&p->sighand->siglock);
timer->it_status = POSIX_TIMER_ARMED;
if (unlikely(!task_can_enqueue_timer(p, clock_pid_type(timer->it_clock))))
return;
if (!cpu_timer_enqueue(&base->tqhead, ctmr))
return;