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@xxxxxxxxxxxxxxx Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> --- mm/shmem.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- 4.7-rc6/mm/shmem.c 2016-06-26 22:02:27.543373427 -0700 +++ linux/mm/shmem.c 2016-07-10 15:19:24.000000000 -0700 @@ -2225,9 +2225,11 @@ static long shmem_fallocate(struct file 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; } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>