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