On Monday 21 Mar 2016 11:00:14 Chris Mason wrote: > Hi everyone, > > I realized last week that CONFIG_DEBUG_PAGEALLOC had dropped out of my > config, and hit a crash inside __btrfs_lookup_bio_sums once I enabled it > again. It's hard for this bug to cause problems because Chandan's inner > loop is always done at the same time the outer loop is done. Without my > goto, it's just exiting normally, but only after reading bvec->bv_len > (which isn't valid). > > I have this on top of my integration-4.6. Once things pass I'll > send a pull later today or Tuesday morning: > > Commit c40a3d38aff4e1c (Btrfs: Compute and look up csums based on > sectorsized blocks) changes around how we walk the bios while looking up > crcs. There's an inner loop that is jumping to the next bvec based on > sectors and before it derefs the next bvec, it needs to make sure we're > still in the bio. > > In this case, the outer loop would have decided to stop moving forward > too, and the bvec deref is never actually used for anything. But > CONFIG_DEBUG_PAGEALLOC catches it because we're outside our bio. >
Chris, Thanks for finding the issue and fixing it. From now onwards, I will make sure that I have CONFIG_DEBUG_PAGEALLOC enabled on my test kernel build config. Reviewed-by: Chandan Rajendra <[email protected]> -- chandan -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
