On Mon, Aug 07 2017, Dominik Brodowski wrote: > Neil, Shaohua, > > following up on David R's bug message: I have observed something similar > on v4.12.[345] and v4.13-rc4, but not on v4.11. This is a RAID1 (on bare > metal partitions, /dev/sdaX and /dev/sdbY linked together). In case it > matters: Further upwards are cryptsetup, a DM volume group, then logical > volumes, and then filesystems (ext4, but also happened with xfs). > > In a tedious bisect (the bug wasn't as quickly reproducible as I would like, > but happened when I repeatedly created large lvs and filled them with some > content, while compiling kernels in parallel), I was able to track this > down to: > > > commit 4ad23a976413aa57fe5ba7a25953dc35ccca5b71 > Author: NeilBrown <neilb@xxxxxxxx> > Date: Wed Mar 15 14:05:14 2017 +1100 > > MD: use per-cpu counter for writes_pending > > The 'writes_pending' counter is used to determine when the > array is stable so that it can be marked in the superblock > as "Clean". Consequently it needs to be updated frequently > but only checked for zero occasionally. Recent changes to > raid5 cause the count to be updated even more often - once > per 4K rather than once per bio. This provided > justification for making the updates more efficient. > > ... Thanks for the report... and for bisecting and for re-sending... I believe I have found the problem, and have sent a patch separately. If mddev->safemode == 1 and mddev->in_sync != 0, md_check_recovery() causes the thread that calls it to spin. Prior to the patch you found, that couldn't happen. Now it can, so it needs to be handled more carefully. While I was examining the code, I found another bug - so that is a win! Thanks, NeilBrown
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