+ mm-optimize-the-redundant-loop-of-mm_update_owner_next.patch added to mm-hotfixes-unstable branch

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The patch titled
     Subject: mm: optimize the redundant loop of mm_update_owner_next()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-optimize-the-redundant-loop-of-mm_update_owner_next.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-optimize-the-redundant-loop-of-mm_update_owner_next.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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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Jinliang Zheng <alexjlzheng@xxxxxxxxxxx>
Subject: mm: optimize the redundant loop of mm_update_owner_next()
Date: Thu, 20 Jun 2024 20:21:24 +0800

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@xxxxxxxxxxx
Signed-off-by: Jinliang Zheng <alexjlzheng@xxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Tycho Andersen <tandersen@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/exit.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/exit.c~mm-optimize-the-redundant-loop-of-mm_update_owner_next
+++ a/kernel/exit.c
@@ -484,6 +484,8 @@ retry:
 	 * 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) {
_

Patches currently in -mm which might be from alexjlzheng@xxxxxxxxxxx are

mm-optimize-the-redundant-loop-of-mm_update_owner_next.patch





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