Patch "mm/thp: do not wait for lock_page() in deferred_split_scan()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

mm/thp: do not wait for lock_page() in deferred_split_scan()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-thp-do-not-wait-for-lock_page-in-deferred_split_scan.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Kirill A. Shutemov" <[email protected]>
Date: Thu, 22 Mar 2018 16:17:31 -0700
Subject: mm/thp: do not wait for lock_page() in deferred_split_scan()

From: Kirill A. Shutemov <[email protected]>

commit fa41b900c30b45fab03783724932dc30cd46a6be upstream.

deferred_split_scan() gets called from reclaim path. Waiting for page lock may lead to deadlock there.

Replace lock_page() with trylock_page() and skip the page if we failed to lock it. We will get to the page on the next scan.

---
 mm/huge_memory.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

@@ -2279,11 +2279,13 @@ static unsigned long deferred_split_scan
 
 	list_for_each_safe(pos, next, &list) {
 		page = list_entry((void *)pos, struct page, mapping);
-		lock_page(page);
+		if (!trylock_page(page))
+			goto next;
 		/* split_huge_page() removes page from list on success */
 		if (!split_huge_page(page))
 			split++;
 		unlock_page(page);
+next:
 		put_page(page);
 	}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mm-khugepaged.c-convert-vm_bug_on-to-collapse-fail.patch queue-4.9/mm-thp-do-not-wait-for-lock_page-in-deferred_split_scan.patch queue-4.9/mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_huge_shrink.patch