[PATCH v4 1/3] md: suspend array before raid10 reshape via sync_action

["Chen Cheng" <chencheng@fnnas.com>]

From: Chen Cheng <chencheng@fnnas.com>

The sync_action=reshape path currently enters mddev_start_reshape() with
reconfig_mutex held but without suspending the array first. For raid10,
that means raid10_start_reshape() has to drop reconfig_mutex and reacquire
the array through mddev_suspend_and_lock_nointr() before it can safely
switch geometry-dependent state.

Use mddev_suspend_and_lock() for ACTION_RESHAPE in action_store(), so
the sysfs reshape path reaches mddev_start_reshape() with the array
already suspended and locked.

Other sync_action operations keep using mddev_lock() unchanged.

Signed-off-by: Chen Cheng <chencheng@fnnas.com>
---
 drivers/md/md.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 096bb64e87bd..5bc937e149ac 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5256,30 +5256,39 @@ static int mddev_start_reshape(struct mddev *mddev)
 
 static ssize_t
 action_store(struct mddev *mddev, const char *page, size_t len)
 {
 	int ret;
+	bool suspended = false;
 	enum sync_action action;
 
 	if (!mddev->pers || !mddev->pers->sync_request)
 		return -EINVAL;
 
+	action = md_sync_action_by_name(page);
 retry:
 	if (work_busy(&mddev->sync_work))
 		flush_work(&mddev->sync_work);
 
-	ret = mddev_lock(mddev);
+	if (action == ACTION_RESHAPE) {
+		ret = mddev_suspend_and_lock(mddev);
+		suspended = true;
+	} else {
+		ret = mddev_lock(mddev);
+		suspended = false;
+	}
 	if (ret)
 		return ret;
 
 	if (work_busy(&mddev->sync_work)) {
-		mddev_unlock(mddev);
+		if (suspended)
+			mddev_unlock_and_resume(mddev);
+		else
+			mddev_unlock(mddev);
 		goto retry;
 	}
 
-	action = md_sync_action_by_name(page);
-
 	/* TODO: mdadm rely on "idle" to start sync_thread. */
 	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
 		switch (action) {
 		case ACTION_FROZEN:
 			md_frozen_sync_thread(mddev);
@@ -5344,11 +5353,14 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 	md_wakeup_thread(mddev->thread);
 	sysfs_notify_dirent_safe(mddev->sysfs_action);
 	ret = len;
 
 out:
-	mddev_unlock(mddev);
+	if (suspended)
+		mddev_unlock_and_resume(mddev);
+	else
+		mddev_unlock(mddev);
 	return ret;
 }
 
 static struct md_sysfs_entry md_scan_mode =
 __ATTR_PREALLOC(sync_action, S_IRUGO|S_IWUSR, action_show, action_store);
-- 
2.54.0