FAILED: patch "[PATCH] mm: optimize the redundant loop of mm_update_owner_next()" failed to apply to 4.19-stable tree

FAILED: patch "[PATCH] mm: optimize the redundant loop of mm_update_owner_next()" failed to apply to 4.19-stable tree

[gregkh]

The patch below does not apply to the 4.19-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-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x 76ba6acfcce871db13ad51c6dc8f56fec2e92853
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024073058-game-plant-575c@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

76ba6acfcce8 ("mm: optimize the redundant loop of mm_update_owner_next()")

thanks,

greg k-h

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

From 76ba6acfcce871db13ad51c6dc8f56fec2e92853 Mon Sep 17 00:00:00 2001
From: Jinliang Zheng <alexjlzheng@tencent.com>
Date: Thu, 20 Jun 2024 20:21:24 +0800
Subject: [PATCH] mm: optimize the redundant loop of mm_update_owner_next()

When mm_update_owner_next() is racing with swapoff (try_to_unuse()) or
/proc or ptrace or page migration (get_task_mm()), it is impossible to
find an appropriate task_struct in the loop whose mm_struct is the same as
the target mm_struct.

If the above race condition is combined with the stress-ng-zombie and
stress-ng-dup tests, such a long loop can easily cause a Hard Lockup in
write_lock_irq() for tasklist_lock.

Recognize this situation in advance and exit early.

Link: https://lkml.kernel.org/r/20240620122123.3877432-1-alexjlzheng@tencent.com
Signed-off-by: Jinliang Zheng <alexjlzheng@tencent.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tycho Andersen <tandersen@netflix.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/exit.c b/kernel/exit.c
index f95a2c1338a8..81fcee45d630 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -484,6 +484,8 @@ void mm_update_next_owner(struct mm_struct *mm)
 	 * Search through everything else, we should not get here often.
 	 */
 	for_each_process(g) {
+		if (atomic_read(&mm->mm_users) <= 1)
+			break;
 		if (g->flags & PF_KTHREAD)
 			continue;
 		for_each_thread(g, c) {