Patch "tmpfs: fix regression hang in fallocate undo" has been added to the 4.4-stable tree

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

tmpfs: fix regression hang in fallocate undo

to the 4.4-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:
tmpfs-fix-regression-hang-in-fallocate-undo.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Hugh Dickins <[email protected]>
Date: Sun, 10 Jul 2016 16:46:32 -0700
Subject: tmpfs: fix regression hang in fallocate undo

From: Hugh Dickins <[email protected]>

commit 7f556567036cb7f89aabe2f0954b08566b4efb53 upstream.

The well-spotted fallocate undo fix is good in most cases, but not when fallocate failed on the very first page. index 0 then passes lend -1 to shmem_undo_range(), and that has two bad effects: (a) that it will undo every fallocation throughout the file, unrestricted by the current range; but more importantly (b) it can cause the undo to hang, because lend -1 is treated as truncation, which makes it keep on retrying until every page has gone, but those already fully instantiated will never go away. Big thank you to xfstests generic/269 which demonstrates this.

---
 mm/shmem.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

@@ -2153,9 +2153,11 @@ static long shmem_fallocate(struct file
 									NULL);
 		if (error) {
 			/* Remove the !PageUptodate pages we added */
-			shmem_undo_range(inode,
-				(loff_t)start << PAGE_CACHE_SHIFT,
-				((loff_t)index << PAGE_CACHE_SHIFT) - 1, true);
+			if (index > start) {
+				shmem_undo_range(inode,
+				 (loff_t)start << PAGE_CACHE_SHIFT,
+				 ((loff_t)index << PAGE_CACHE_SHIFT) - 1, true);
+			}
 			goto undone;
 		}
 

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

queue-4.4/tmpfs-fix-regression-hang-in-fallocate-undo.patch queue-4.4/tmpfs-don-t-undo-fallocate-past-its-last-page.patch