Re: [dm-devel] [PATCH -next v2 3/6] md: add a mutex to synchronize idle and frozen in action_store()

[Xiao Ni]

在 2023/5/29 下午9:20, Yu Kuai 写道:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> ---
>   drivers/md/md.c | 5 +++++
>   drivers/md/md.h | 3 +++
>   2 files changed, 8 insertions(+)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 23e8e7eae062..63a993b52cd7 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -644,6 +644,7 @@ void mddev_init(struct mddev *mddev)
>   	mutex_init(&mddev->open_mutex);
>   	mutex_init(&mddev->reconfig_mutex);
>   	mutex_init(&mddev->delete_mutex);
> +	mutex_init(&mddev->sync_mutex);
>   	mutex_init(&mddev->bitmap_info.mutex);
>   	INIT_LIST_HEAD(&mddev->disks);
>   	INIT_LIST_HEAD(&mddev->all_mddevs);
> @@ -4785,14 +4786,18 @@ 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_init(&mddev->delete_mutex);


typo error? It should be mutex_lock(&mddev->sync_mutex); ?

Regards

Xiao

>   	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 bfd2306bc750..2fa903de5bd0 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -537,6 +537,9 @@ struct mddev {
>   	/* Protect the deleting list */
>   	struct mutex			delete_mutex;
>   
> +	/* 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;