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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: b9b4bb26af ("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>
This commit is contained in:
Hugh Dickins 2016-07-10 16:46:32 -07:00 committed by Linus Torvalds
parent 617a8d6bc1
commit 7f55656703
1 changed files with 5 additions and 3 deletions
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8
mm/shmem.c
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@ -2225,9 +2225,11 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
error = shmem_getpage(inode, index, &page, SGP_FALLOC);
if (error) {
/* Remove the !PageUptodate pages we added */
shmem_undo_range(inode,
(loff_t)start << PAGE_SHIFT,
((loff_t)index << PAGE_SHIFT) - 1, true);
if (index > start) {
shmem_undo_range(inode,
(loff_t)start << PAGE_SHIFT,
((loff_t)index << PAGE_SHIFT) - 1, true);
}
goto undone;
}