tree 020fc68e31c9361c49786606a819dc5be9a2a8a6
parent 617a8d6bc19edd075e8111c6770f79cae75be51f
author Hugh Dickins <hughd@google.com> 1468194392 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1468206524 -0700

tmpfs: fix regression hang in fallocate undo

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>