On Wed, Mar 22, 2023 at 11:32 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote: > > Hi, > > 在 2023/03/23 11:50, Guoqing Jiang 写道: > > > Combined your debug patch with above steps. Seems you are > > > > 1. add delay to action_store, so it can't get lock in time. > > 2. echo "want_replacement"**triggers md_check_recovery which can grab lock > > to start sync thread. > > 3. action_store finally hold lock to clear RECOVERY_RUNNING in reap sync > > thread. > > 4. Then the new added BUG_ON is invoked since RECOVERY_RUNNING is cleared > > in step 3. > > Yes, this is exactly what I did. > > > sync_thread can be interrupted once MD_RECOVERY_INTR is set which means > > the RUNNING > > can be cleared, so I am not sure the added BUG_ON is reasonable. And > > change BUG_ON > > I think BUG_ON() is reasonable because only md_reap_sync_thread can > clear it, md_do_sync will exit quictly if MD_RECOVERY_INTR is set, but > md_do_sync should not see that MD_RECOVERY_RUNNING is cleared, otherwise > there is no gurantee that only one sync_thread can be in progress. > > > like this makes more sense to me. > > > > +BUG_ON(!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) && > > +!test_bit(MD_RECOVERY_INTR, &mddev->recovery)); > > I think this can be reporduced likewise, md_check_recovery clear > MD_RECOVERY_INTR, and new sync_thread triggered by echo > "want_replacement" won't set this bit. > > > > > I think there might be racy window like you described but it should be > > really small, I prefer > > to just add a few lines like this instead of revert and introduce new > > lock to resolve the same > > issue (if it is). > > The new lock that I add in this patchset is just try to synchronize idle > and forzen from action_store（patch 3), I can drop it if you think this > is not necessary. > > The main changes is patch 4, new lines is not much and I really don't > like to add new flags unless we have to, current code is already hard > to understand... > > By the way, I'm concerned that drop the mutex to unregister sync_thread > might not be safe, since the mutex protects lots of stuff, and there > might exist other implicit dependencies. > > > > > TBH, I am reluctant to see the changes in the series, it can only be > > considered > > acceptable with conditions: > > > > 1. the previous raid456 bug can be fixed in this way too, hopefully Marc > > or others > > can verify it. > > 2. pass all the tests in mdadm AFAICT, this set looks like a better solution for this problem. But I agree that we need to make sure it fixes the original bug. mdadm tests are not in a very good shape at the moment. I will spend more time to look into these tests. Thanks, Song
