md: add a mutex to synchronize idle and frozen in action_store()

Currently, for idle and frozen, action_store will hold 'reconfig_mutex'
and call md_reap_sync_thread() to stop sync thread, however, this will
cause deadlock (explained in the next patch). In order to fix the
problem, following patch will release 'reconfig_mutex' and wait on
'resync_wait', like md_set_readonly() and do_md_stop() does.

Consider that action_store() will set/clear 'MD_RECOVERY_FROZEN'
unconditionally, which might cause unexpected problems, for example,
frozen just set 'MD_RECOVERY_FROZEN' and is still in progress, while
'idle' clear 'MD_RECOVERY_FROZEN' and new sync thread is started, which
might starve in progress frozen. A mutex is added to synchronize idle
and frozen from action_store().

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230529132037.2124527-4-yukuai1@huaweicloud.com

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 7fa91f0..3d7e87c 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -643,6 +643,7 @@ void mddev_init(struct mddev *mddev)
 {
        mutex_init(&mddev->open_mutex);
        mutex_init(&mddev->reconfig_mutex);
+       mutex_init(&mddev->sync_mutex);
        mutex_init(&mddev->bitmap_info.mutex);
        INIT_LIST_HEAD(&mddev->disks);
        INIT_LIST_HEAD(&mddev->all_mddevs);
@@ -4777,14 +4778,18 @@ static void stop_sync_thread(struct mddev *mddev)
 
 static void idle_sync_thread(struct mddev *mddev)
 {
+       mutex_lock(&mddev->sync_mutex);
        clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
        stop_sync_thread(mddev);
+       mutex_unlock(&mddev->sync_mutex);
 }
 
 static void frozen_sync_thread(struct mddev *mddev)
 {
+       mutex_lock(&mddev->sync_mutex);
        set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
        stop_sync_thread(mddev);
+       mutex_unlock(&mddev->sync_mutex);
 }
 
 static ssize_t

diff --git a/drivers/md/md.h b/drivers/md/md.h
index 1aef86b..18c168b 100644 (file)
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -535,6 +535,9 @@ struct mddev {
         */
        struct list_head                deleting;
 
+       /* Used to synchronize idle and frozen for action_store() */
+       struct mutex                    sync_mutex;
+
        bool    has_superblocks:1;
        bool    fail_last_dev:1;
        bool    serialize_policy:1;