We've switched to cloned bios in btrfs and hit a nasty bug leading to corruptions, when cloned bios are iterated by bio_for_each_segment_all.
Report and fix: https://patchwork.kernel.org/patch/9838535/ As a matter of precaution, we've added assertions to btrfs code to catch the bad usage pattern: https://patchwork.kernel.org/patch/9839267/ The cloned/bi_vcnt behaviour seems tobe implementation dependent and is not documented, so this patch at least warns about this one particular case but this might still be insufficient. CC: linux-block@vger.kernel.org Signed-off-by: David Sterba <dste...@suse.com> --- include/linux/bio.h | 3 +++ 1 file changed, 3 insertions(+) diff --git a/include/linux/bio.h b/include/linux/bio.h index 7b1cf4ba0902..f1ac84edcf39 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -156,6 +156,9 @@ static inline void *bio_data(struct bio *bio) /* * drivers should _never_ use the all version - the bio may have been split * before it got to the driver and the driver won't own all of it + * + * Note that cloned bios must not use this as their bi_vcnt may be invalid and + * this could lead to silent corruptions. */ #define bio_for_each_segment_all(bvl, bio, i) \ for (i = 0, bvl = (bio)->bi_io_vec; i < (bio)->bi_vcnt; i++, bvl++) -- 2.13.0
