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

From: Yu Kuai <yukuai1@huaweicloud.com>
To: guoqing.jiang@linux.dev, logang@deltatee.com,
	pmenzel@molgen.mpg.de, agk@redhat.com, snitzer@kernel.org,
	song@kernel.org
Cc: linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org,
	yukuai3@huawei.com, yukuai1@huaweicloud.com, yi.zhang@huawei.com,
	yangerkun@huawei.com
Subject: [PATCH -next 3/6] md: add a mutex to synchronize idle and frozen in action_store()
Date: Wed, 22 Mar 2023 14:41:19 +0800	[thread overview]
Message-ID: <20230322064122.2384589-4-yukuai1@huaweicloud.com> (raw)
In-Reply-To: <20230322064122.2384589-1-yukuai1@huaweicloud.com>

From: Yu Kuai <yukuai3@huawei.com>

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.

This patch add a mutex to synchronize idle and frozen from
action_store().

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 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 076936fee65a..223c03149852 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -656,6 +656,7 @@ void mddev_init(struct mddev *mddev)
 	mutex_init(&mddev->open_mutex);
 	mutex_init(&mddev->reconfig_mutex);
 	mutex_init(&mddev->bitmap_info.mutex);
+	mutex_init(&mddev->sync_mutex);
 	INIT_LIST_HEAD(&mddev->disks);
 	INIT_LIST_HEAD(&mddev->all_mddevs);
 	timer_setup(&mddev->safemode_timer, md_safemode_timeout, 0);
@@ -4783,14 +4784,18 @@ 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 e148e3c83b0d..64474e458545 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -534,6 +534,9 @@ struct mddev {
 	bool	has_superblocks:1;
 	bool	fail_last_dev:1;
 	bool	serialize_policy:1;
+
+	/* Used to synchronize idle and frozen for action_store() */
+	struct mutex sync_mutex;
 };
 
 enum recovery_flags {
-- 
2.31.1

