+ exit-wait_task_zombie-kill-the-no-longer-necessary-spin_lock_irqsiglock.patch added to mm-hotfixes-unstable branch

+ exit-wait_task_zombie-kill-the-no-longer-necessary-spin_lock_irqsiglock.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: exit: wait_task_zombie: kill the no longer necessary spin_lock_irq(siglock)
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     exit-wait_task_zombie-kill-the-no-longer-necessary-spin_lock_irqsiglock.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/exit-wait_task_zombie-kill-the-no-longer-necessary-spin_lock_irqsiglock.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Oleg Nesterov <oleg@redhat.com>
Subject: exit: wait_task_zombie: kill the no longer necessary spin_lock_irq(siglock)
Date: Tue, 23 Jan 2024 16:34:00 +0100

After the recent changes nobody use siglock to read the values protected
by stats_lock, we can kill spin_lock_irq(&current->sighand->siglock) and
update the comment.

With this patch only __exit_signal() and thread_group_start_cputime() take
stats_lock under siglock.

Link: https://lkml.kernel.org/r/20240123153359.GA21866@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Dylan Hatch <dylanbhatch@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/exit.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

--- a/kernel/exit.c~exit-wait_task_zombie-kill-the-no-longer-necessary-spin_lock_irqsiglock
+++ a/kernel/exit.c
@@ -1127,17 +1127,14 @@ static int wait_task_zombie(struct wait_
 		 * and nobody can change them.
 		 *
 		 * psig->stats_lock also protects us from our sub-threads
-		 * which can reap other children at the same time. Until
-		 * we change k_getrusage()-like users to rely on this lock
-		 * we have to take ->siglock as well.
+		 * which can reap other children at the same time.
 		 *
 		 * We use thread_group_cputime_adjusted() to get times for
 		 * the thread group, which consolidates times for all threads
 		 * in the group including the group leader.
 		 */
 		thread_group_cputime_adjusted(p, &tgutime, &tgstime);
-		spin_lock_irq(&current->sighand->siglock);
-		write_seqlock(&psig->stats_lock);
+		write_seqlock_irq(&psig->stats_lock);
 		psig->cutime += tgutime + sig->cutime;
 		psig->cstime += tgstime + sig->cstime;
 		psig->cgtime += task_gtime(p) + sig->gtime + sig->cgtime;
@@ -1160,8 +1157,7 @@ static int wait_task_zombie(struct wait_
 			psig->cmaxrss = maxrss;
 		task_io_accounting_add(&psig->ioac, &p->ioac);
 		task_io_accounting_add(&psig->ioac, &sig->ioac);
-		write_sequnlock(&psig->stats_lock);
-		spin_unlock_irq(&current->sighand->siglock);
+		write_sequnlock_irq(&psig->stats_lock);
 	}
 
 	if (wo->wo_rusage)
_

Patches currently in -mm which might be from oleg@redhat.com are

getrusage-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch
getrusage-use-sig-stats_lock-rather-than-lock_task_sighand.patch
fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch
fs-proc-do_task_stat-use-sig-stats_lock-to-gather-the-threads-children-stats.patch
exit-wait_task_zombie-kill-the-no-longer-necessary-spin_lock_irqsiglock.patch
ptrace_attach-shift-sendsigstop-into-ptrace_set_stopped.patch