Song Liu <song@xxxxxxxxxx> 于2021年2月11日周四 上午8:31写道: > > On Tue, Feb 9, 2021 at 6:22 PM Guoqing Jiang > <guoqing.jiang@xxxxxxxxxxxxxxx> wrote: > > > > 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: > > issu://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@xxxxxxxxxxxxx/T/#t > > > > Reported-and-tested-by: Donald Buczek <buczek@xxxxxxxxxxxxx> > > Signed-off-by: Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx> > > Thanks for debugging the issue. However, I am not sure whether this is > the proper > fix. For example, would this break dm-raid.c:raid_message()? IIUC, > raid_message() > calls md_reap_sync_thread() without holding reconfigure_mutex, no? > > Thanks, > Song. right. A simple solution would be add a parameter to md_reap_sync_thread to indicate if a reconfigure_mutex lock is held. Regards! Jack > > > --- > > drivers/md/md.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/drivers/md/md.c b/drivers/md/md.c > > index ca40942..eec8c27 100644 > > --- a/drivers/md/md.c > > +++ b/drivers/md/md.c > > @@ -9365,13 +9365,18 @@ void md_check_recovery(struct mddev *mddev) > > EXPORT_SYMBOL(md_check_recovery); > > > > void md_reap_sync_thread(struct mddev *mddev) > > + __releases(&mddev->reconfig_mutex) > > + __acquires(&mddev->reconfig_mutex) > > + > > { > > struct md_rdev *rdev; > > sector_t old_dev_sectors = mddev->dev_sectors; > > bool is_reshaped = false; > > > > /* resync has finished, collect result */ > > + mddev_unlock(mddev); > > md_unregister_thread(&mddev->sync_thread); > > + mddev_lock_nointr(mddev); > > if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery) && > > !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) && > > mddev->degraded != mddev->raid_disks) { > > -- > > 2.7.4 > >