From: NeilBrown neilb@suse.com
commit 35bfc52187f6df8779d0f1cebdb52b7f797baf4e upstream
There are various deadlocks that can occur when a thread holds reconfig_mutex and calls ->quiesce(mddev, 1). As some write request block waiting for metadata to be updated (e.g. to record device failure), and as the md thread updates the metadata while the reconfig mutex is held, holding the mutex can stop write requests completing, and this prevents ->quiesce(mddev, 1) from completing.
->quiesce() is now usually called from mddev_suspend(), and it is always called with reconfig_mutex held. So at this time it is safe for the thread to update metadata without explicitly taking the lock.
So add 2 new flags, one which says the unlocked updates is allowed, and one which ways it is happening. Then allow it while the quiesce completes, and then wait for it to finish.
Reported-and-tested-by: Xiao Ni xni@redhat.com Signed-off-by: NeilBrown neilb@suse.com Signed-off-by: Shaohua Li shli@fb.com [jwang: cherry-pick to 4.14] Signed-off-by: Jack Wang jinpu.wang@profitbricks.com --- drivers/md/md.c | 14 ++++++++++++++ drivers/md/md.h | 6 ++++++ 2 files changed, 20 insertions(+)
diff --git a/drivers/md/md.c b/drivers/md/md.c index 56e180b..ceee5f5 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -364,8 +364,12 @@ void mddev_suspend(struct mddev *mddev) return; synchronize_rcu(); wake_up(&mddev->sb_wait); + set_bit(MD_ALLOW_SB_UPDATE, &mddev->flags); + smp_mb__after_atomic(); wait_event(mddev->sb_wait, atomic_read(&mddev->active_io) == 0); mddev->pers->quiesce(mddev, 1); + clear_bit_unlock(MD_ALLOW_SB_UPDATE, &mddev->flags); + wait_event(mddev->sb_wait, !test_bit(MD_UPDATING_SB, &mddev->flags));
del_timer_sync(&mddev->safemode_timer); } @@ -8880,6 +8884,16 @@ void md_check_recovery(struct mddev *mddev) unlock: wake_up(&mddev->sb_wait); mddev_unlock(mddev); + } else if (test_bit(MD_ALLOW_SB_UPDATE, &mddev->flags) && mddev->sb_flags) { + /* Write superblock - thread that called mddev_suspend() + * holds reconfig_mutex for us. + */ + set_bit(MD_UPDATING_SB, &mddev->flags); + smp_mb__after_atomic(); + if (test_bit(MD_ALLOW_SB_UPDATE, &mddev->flags)) + md_update_sb(mddev, 0); + clear_bit_unlock(MD_UPDATING_SB, &mddev->flags); + wake_up(&mddev->sb_wait); } } EXPORT_SYMBOL(md_check_recovery); diff --git a/drivers/md/md.h b/drivers/md/md.h index 9b0a896..37c19b7 100644 --- a/drivers/md/md.h +++ b/drivers/md/md.h @@ -237,6 +237,12 @@ enum mddev_flags { */ MD_HAS_PPL, /* The raid array has PPL feature set */ MD_HAS_MULTIPLE_PPLS, /* The raid array has multiple PPLs feature set */ + MD_ALLOW_SB_UPDATE, /* md_check_recovery is allowed to update + * the metadata without taking reconfig_mutex. + */ + MD_UPDATING_SB, /* md_check_recovery is updating the metadata + * without explicitly holding reconfig_mutex. + */ };
enum mddev_sb_flags {