The following commit has been merged into the timers/urgent branch of tip:

Commit-ID: 63dffecfba3eddcf67a8f76d80e0c141f93d44a5 Gitweb: https://git.kernel.org/tip/63dffecfba3eddcf67a8f76d80e0c141f93d44a5 Author: Frederic Weisbecker frederic@kernel.org AuthorDate: Sat, 23 Nov 2024 00:48:11 +01:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Fri, 29 Nov 2024 13:19:09 +01:00

posix-timers: Target group sigqueue to current task only if not exiting

A sigqueue belonging to a posix timer, which target is not a specific thread but a whole thread group, is preferrably targeted to the current task if it is part of that thread group.

However nothing prevents a posix timer event from queueing such a sigqueue from a reaped yet running task. The interruptible code space between exit_notify() and the final call to schedule() is enough for posix_timer_fn() hrtimer to fire.

If that happens while the current task is part of the thread group target, it is proposed to handle it but since its sighand pointer may have been cleared already, the sigqueue is dropped even if there are other tasks running within the group that could handle it.

As a result posix timers with thread group wide target may miss signals when some of their threads are exiting.

Fix this with verifying that the current task hasn't been through exit_notify() before proposing it as a preferred target so as to ensure that its sighand is still here and stable.

complete_signal() might still reconsider the choice and find a better target within the group if current has passed retarget_shared_pending() already.

Fixes: bcb7ee79029d ("posix-timers: Prefer delivery of signals to the current thread") Reported-by: Anthony Mallet anthony.mallet@laas.fr Suggested-by: Oleg Nesterov oleg@redhat.com Signed-off-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Acked-by: Oleg Nesterov oleg@redhat.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20241122234811.60455-1-frederic@kernel.org Closes: https://lore.kernel.org/all/26411.57288.238690.681680@gargle.gargle.HOWL --- kernel/signal.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c index 98b65cb..989b1cc 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1959,14 +1959,15 @@ static void posixtimer_queue_sigqueue(struct sigqueue *q, struct task_struct *t, * * Where type is not PIDTYPE_PID, signals must be delivered to the * process. In this case, prefer to deliver to current if it is in - * the same thread group as the target process, which avoids - * unnecessarily waking up a potentially idle task. + * the same thread group as the target process and its sighand is + * stable, which avoids unnecessarily waking up a potentially idle task. */ static inline struct task_struct *posixtimer_get_target(struct k_itimer *tmr) { struct task_struct *t = pid_task(tmr->it_pid, tmr->it_pid_type);

- if (t && tmr->it_pid_type != PIDTYPE_PID && same_thread_group(t, current)) + if (t && tmr->it_pid_type != PIDTYPE_PID && + same_thread_group(t, current) && !current->exit_state) t = current; return t; }