From: David Sterba dsterba@suse.com
[ Upstream commit 4babad10198fa73fe73239d02c2e99e3333f5f5c ]
Dan's smatch tool reports
fs/btrfs/file-item.c:295 btrfs_lookup_bio_sums() warn: should this be 'count == -1'
which points to the while (count--) loop. With count == 0 the check itself could decrement it to -1. There's a WARN_ON a few lines below that has never been seen in practice though.
It turns out that the value of page_bytes_left matches the count (by sectorsize multiples). The loop never reaches the state where count would go to -1, because page_bytes_left == 0 is found first and this breaks out.
For clarity, use only plain check on count (and only for positive value), decrement safely inside the loop. Any other discrepancy after the whole bio list processing should be reported by the exising WARN_ON_ONCE as well.
Reported-by: Dan Carpenter dan.carpenter@oracle.com Reviewed-by: Josef Bacik josef@toxicpanda.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- fs/btrfs/file-item.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c index 4cf2817..f9e280d 100644 --- a/fs/btrfs/file-item.c +++ b/fs/btrfs/file-item.c @@ -275,7 +275,8 @@ static blk_status_t __btrfs_lookup_bio_sums(struct inode *inode, struct bio *bio csum += count * csum_size; nblocks -= count; next: - while (count--) { + while (count > 0) { + count--; disk_bytenr += fs_info->sectorsize; offset += fs_info->sectorsize; page_bytes_left -= fs_info->sectorsize;