Commit 52a8202d authored Jul 10, 2016 by Hugh Dickins Committed by Sasha Levin Jul 12, 2016

tmpfs: fix regression hang in fallocate undo



[ Upstream commit 7f556567036cb7f89aabe2f0954b08566b4efb53 ]

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.

Fixes: b9b4bb26af01 ("tmpfs: don't undo fallocate past its last page")
Cc: stable@vger.kernel.org
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

parent 6a9f9d4e

mm/shmem.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -2140,9 +2140,11 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
		NULL);
		if (error) {
		/* Remove the !PageUptodate pages we added */
		if (index > start) {
		shmem_undo_range(inode,
		(loff_t)start << PAGE_CACHE_SHIFT,
		((loff_t)index << PAGE_CACHE_SHIFT) - 1, true);
		}
		goto undone;
		}