[PATCH] md: Fix badness in sysfs_notify caused by md_new_event

From: NeilBrown <[e-mail]>

If an error is reported by a drive in a RAID array (which is done via
bi_end_io - in interrupt context), we call md_error and md_new_event which
calls sysfs_notify. However sysfs_notify grabs a mutex and so cannot be
called in interrupt context.

This patch just creates a variant of md_new_event which avoids the sysfs
call, and uses that. A better fix for later is to arrange for the event to
be called from user-context.

Note: avoiding the sysfs call isn't a problem as an error will not, by
itself, modify the sync_action attribute. (We do still need to
wake_up(&md_event_waiters) as an error by itself will modify /proc/mdstat).

Signed-off-by: Neil Brown <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/md/md.c

···
 }
 EXPORT_SYMBOL_GPL(md_new_event);
 
+/* Alternate version that can be called from interrupts
+ * when calling sysfs_notify isn't needed.
+ */
+void md_new_event_inintr(mddev_t *mddev)
+{
+	atomic_inc(&md_event_count);
+	wake_up(&md_event_waiters);
+}
+
 /*
  * Enables to iterate over all existing md arrays
  * all_mddevs_lock protects this list.
···
 	set_bit(MD_RECOVERY_INTR, &mddev->recovery);
 	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
 	md_wakeup_thread(mddev->thread);
-	md_new_event(mddev);
+	md_new_event_inintr(mddev);
 }
 
 /* seq_file implementation /proc/mdstat */