mm/shmem: fix truncation of files containing only swapin-error markers

It might not be very common, but we can end up with shmem files that are
composed only of swapin-error/poison markers.

Such markers are not counted in info->alloced. Consequently,
shmem_setattr() can skip shmem_truncate_range(), leaving the markers
behind.

Truncating the file to zero and growing it again will result in reads
failing with -EIO instead of returning zeroes.

Check whether the mapping contains entries, in addition to
info->alloced, before skipping the truncation. Keep the info->alloced
check so that shmem_recalc_inode(), called at the end of
shmem_undo_range(), can fix up accounting after reclaim has emptied the
mapping.

Fixes: 6cec2b95dadf ("mm/shmem: fix infinite loop when swap in shmem error at swapoff time")
Cc: stable@vger.kernel.org
Tested-by: Gregory Price (Meta) <gourry@gourry.net>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Link: https://patch.msgid.link/20261029-fixes_shmem-v4-15-392fc715d8f6@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>

0 files changed, 0 insertions, 0 deletions