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. Reported-by: Donald Buczek <buczek@xxxxxxxxxxxxx> Signed-off-by: Guoqing Jiang <guoqing.jiang@xxxxxxxxx> --- drivers/md/md.c | 9 ++++++++- drivers/md/md.h | 5 +++++ 2 files changed, 13 insertions(+), 1 deletion(-) diff --git a/drivers/md/md.c b/drivers/md/md.c index 309b3af906ad..525f65682356 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -9432,10 +9432,17 @@ void md_reap_sync_thread(struct mddev *mddev) { struct md_rdev *rdev; sector_t old_dev_sectors = mddev->dev_sectors; - bool is_reshaped = false; + bool is_reshaped = false, is_locked = false; + if (mddev_is_locked(mddev)) { + is_locked = true; + mddev_unlock(mddev); + } /* resync has finished, collect result */ md_unregister_thread(&mddev->sync_thread); + if (is_locked) + mddev_lock_nointr(mddev); + if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery) && !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) && mddev->degraded != mddev->raid_disks) { diff --git a/drivers/md/md.h b/drivers/md/md.h index 6ac283864533..af6f3978b62b 100644 --- a/drivers/md/md.h +++ b/drivers/md/md.h @@ -549,6 +549,11 @@ static inline int mddev_trylock(struct mddev *mddev) } extern void mddev_unlock(struct mddev *mddev); +static inline int mddev_is_locked(struct mddev *mddev) +{ + return mutex_is_locked(&mddev->reconfig_mutex); +} + static inline void md_sync_acct(struct block_device *bdev, unsigned long nr_sectors) { atomic_add(nr_sectors, &bdev->bd_disk->sync_io); -- 2.31.1
