[PATCH v4 2/9] md: serialize md_error()

[Kenta Akagi <k@mgml.me>]

md_error is mainly called when a bio fails, so it can run in parallel.
Each personality’s error_handler locks with device_lock, so concurrent
calls are safe.

However, RAID1 and RAID10 require changes for Failfast bio error handling,
which needs a special helper for md_error. For that helper to work, the
regular md_error must also be serialized.

The helper function md_bio_failure_error for failfast will be introduced
in a subsequent commit.

This commit serializes md_error for all RAID personalities. While
unnecessary for RAID levels other than 1 and 10, it has no performance
impact as it is a cold path.

Signed-off-by: Kenta Akagi <k@mgml.me>
---
 drivers/md/md.c | 10 +++++++++-
 drivers/md/md.h |  4 ++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 268410b66b83..5607578a6db9 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -705,6 +705,7 @@ int mddev_init(struct mddev *mddev)
 	atomic_set(&mddev->openers, 0);
 	atomic_set(&mddev->sync_seq, 0);
 	spin_lock_init(&mddev->lock);
+	spin_lock_init(&mddev->error_handle_lock);
 	init_waitqueue_head(&mddev->sb_wait);
 	init_waitqueue_head(&mddev->recovery_wait);
 	mddev->reshape_position = MaxSector;
@@ -8262,7 +8263,7 @@ void md_unregister_thread(struct mddev *mddev, struct md_thread __rcu **threadp)
 }
 EXPORT_SYMBOL(md_unregister_thread);
 
-void md_error(struct mddev *mddev, struct md_rdev *rdev)
+void _md_error(struct mddev *mddev, struct md_rdev *rdev)
 {
 	if (!rdev || test_bit(Faulty, &rdev->flags))
 		return;
@@ -8287,6 +8288,13 @@ void md_error(struct mddev *mddev, struct md_rdev *rdev)
 		queue_work(md_misc_wq, &mddev->event_work);
 	md_new_event();
 }
+
+void md_error(struct mddev *mddev, struct md_rdev *rdev)
+{
+	spin_lock(&mddev->error_handle_lock);
+	_md_error(mddev, rdev);
+	spin_unlock(&mddev->error_handle_lock);
+}
 EXPORT_SYMBOL(md_error);
 
 /* seq_file implementation /proc/mdstat */
diff --git a/drivers/md/md.h b/drivers/md/md.h
index ec598f9a8381..5177cb609e4b 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -619,6 +619,9 @@ struct mddev {
 	/* The sequence number for sync thread */
 	atomic_t sync_seq;
 
+	/* Lock for serializing md_error */
+	spinlock_t			error_handle_lock;
+
 	bool	has_superblocks:1;
 	bool	fail_last_dev:1;
 	bool	serialize_policy:1;
@@ -901,6 +904,7 @@ extern void md_write_start(struct mddev *mddev, struct bio *bi);
 extern void md_write_inc(struct mddev *mddev, struct bio *bi);
 extern void md_write_end(struct mddev *mddev);
 extern void md_done_sync(struct mddev *mddev, int blocks, int ok);
+void _md_error(struct mddev *mddev, struct md_rdev *rdev);
 extern void md_error(struct mddev *mddev, struct md_rdev *rdev);
 extern void md_finish_reshape(struct mddev *mddev);
 void md_submit_discard_bio(struct mddev *mddev, struct md_rdev *rdev,
-- 
2.50.1