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...

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

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** 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@tencent.com 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@tencent.com Signed-off-by: Jinliang Zheng alexjlzheng@tencent.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 ---

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@tencent.com are

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