The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 63dffecfba3eddcf67a8f76d80e0c141f93d44a5 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024120657-mushiness-fence-cc2c@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 63dffecfba3eddcf67a8f76d80e0c141f93d44a5 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker frederic@kernel.org Date: Sat, 23 Nov 2024 00:48:11 +0100 Subject: [PATCH] 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

diff --git a/kernel/signal.c b/kernel/signal.c index 98b65cb35830..989b1cc9116a 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; }