loop, zloop: fix dma_alignment for large or unreported limits

A file system sets STATX_DIOALIGN with zeroed alignments when the file
can't be used for direct I/O. The zero underflowed to UINT_MAX and
triggered a queue limits validation warning. Fall back to the block
device's limits when dio_mem_align isn't reported.

A file system with a block size larger than PAGE_SIZE may also report a
memory alignment that can't be expressed as a queue limit. File systems
fall back to buffered I/O for requests that don't meet their alignment,
so cap the reported limit to the largest possible value.

Fixes: 6c8dec275ccc ("loop: set dma_alignment from the backing file for direct I/O")
Fixes: c5059c1af2bd ("zloop: set dma_alignment from the backing files for direct I/O")
Reported-by: syzbot+ac00e7bf7ac8c91af921@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ac00e7bf7ac8c91af921
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260810164218.3721636-1-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

0 files changed, 0 insertions, 0 deletions