From: Yu Kuai <redacted>

Advantages for new apis:
 - reconfig_mutex is not required;
 - the weird logical that suspend array hold 'reconfig_mutex' for
   mddev_check_recovery() to update superblock is not needed;
 - the specail handling, 'pers->prepare_suspend', for raid456 is not
   needed;
 - It's safe to be called at any time once mddev is allocated, and it's
   designed to be used from slow path where array configuration is changed;
 - the new helpers is designed to be called before mddev_lock(), hence
   it support to be interrupted by user as well.

Signed-off-by: Yu Kuai <redacted>
---
 drivers/md/md.c | 102 +++++++++++++++++++++++++++++++++++++++++++++++-
 drivers/md/md.h |   3 ++
 2 files changed, 103 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e460b380143d..a075d03d03d3 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -443,12 +443,22 @@ void mddev_suspend(struct mddev *mddev)
                        lockdep_is_held(&mddev->reconfig_mutex));

        WARN_ON_ONCE(thread && current == thread->tsk);
-       if (mddev->suspended++)
+
+       /* can't concurrent with __mddev_suspend() and __mddev_resume() */
+       mutex_lock(&mddev->suspend_mutex);
+       if (mddev->suspended++) {
+               mutex_unlock(&mddev->suspend_mutex);
                return;