Hi, On 2022-05-10 00:44, Song Liu wrote: > On Mon, May 9, 2022 at 1:09 AM Guoqing Jiang <guoqing.jiang@xxxxxxxxx> wrote: >> On 5/9/22 2:37 PM, Song Liu wrote: >>> On Fri, May 6, 2022 at 4:37 AM Guoqing Jiang<guoqing.jiang@xxxxxxxxx> wrote: >>>> From: Guoqing Jiang<guoqing.jiang@xxxxxxxxxxxxxxx> >>>> >>>> Unregister sync_thread doesn't need to hold reconfig_mutex since it >>>> doesn't reconfigure array. >>>> >>>> And it could cause deadlock problem for raid5 as follows: >>>> >>>> 1. process A tried to reap sync thread with reconfig_mutex held after echo >>>> idle to sync_action. >>>> 2. raid5 sync thread was blocked if there were too many active stripes. >>>> 3. SB_CHANGE_PENDING was set (because of write IO comes from upper layer) >>>> which causes the number of active stripes can't be decreased. >>>> 4. SB_CHANGE_PENDING can't be cleared since md_check_recovery was not able >>>> to hold reconfig_mutex. >>>> >>>> More details in the link: >>>> https://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@xxxxxxxxxxxxx/T/#t >>>> >>>> Let's call unregister thread between mddev_unlock and mddev_lock_nointr >>>> (thanks for the report from kernel test robot<lkp@xxxxxxxxx>) if the >>>> reconfig_mutex is held, and mddev_is_locked is introduced accordingly. >>> mddev_is_locked() feels really hacky to me. It cannot tell whether >>> mddev is locked >>> by current thread. So technically, we can unlock reconfigure_mutex for >>> other thread >>> by accident, no? >> >> I can switch back to V2 if you think that is the correct way to do though no >> one comment about the change in dm-raid. > > I guess v2 is the best at the moment. I pushed a slightly modified v2 to > md-next. > I noticed a clear regression with mdadm tests with this patch in md-next (7e6ba434cc6080). Before the patch, tests 07reshape5intr and 07revert-grow would fail fairly infrequently (about 1 in 4 runs for the former and 1 in 30 runs for the latter). After this patch, both tests always fail. I don't have time to dig into why this is, but it would be nice if someone can at least fix the regression. It is hard to make any progress on these tests if we are continuing to further break them. Logan
