On 5/6/22 1:36 PM, Guoqing Jiang 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.
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);
Hmmm. Can it be excluded, that another task is holding the mutex?
Best
Donald
+ }
/* 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);
--
Donald Buczek
buczek@xxxxxxxxxxxxx
Tel: +49 30 8413 1433
