Patch "md: always clear ->safemode when md_check_recovery gets the mddev lock." has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

    md: always clear ->safemode when md_check_recovery gets the mddev lock.

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
md-always-clear-safemode-when-md_check_recovery-gets-the-mddev-lock.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: NeilBrown <[email protected]>
Date: Tue, 8 Aug 2017 16:56:36 +1000
Subject: md: always clear ->safemode when md_check_recovery gets the mddev lock.

From: NeilBrown <[email protected]>

commit 33182d15c6bf182f7ae32a66ea4a547d979cd6d7 upstream.

If ->safemode == 1, md_check_recovery() will try to get the mddev lock and perform various other checks.
If mddev->in_sync is zero, it will call set_in_sync, and clear ->safemode. However if mddev->in_sync is not zero, ->safemode will not be cleared.

When md_check_recovery() drops the mddev lock, the thread is woken up again. Normally it would just check if there was anything else to do, find nothing, and go to sleep. However as ->safemode was not cleared, it will take the mddev lock again, then wake itself up when unlocking.

This results in an infinite loop, repeatedly calling md_check_recovery(), which RCU or the soft-lockup detector will eventually complain about.

Prior to commit 4ad23a976413 ("MD: use per-cpu counter for writes_pending"), safemode would only be set to one when the writes_pending counter reached zero, and would be cleared again when writes_pending is incremented. Since that patch, safemode is set more freely, but is not reliably cleared.

So in md_check_recovery() clear ->safemode before checking ->in_sync.

---
 drivers/md/md.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -8639,6 +8639,9 @@ void md_check_recovery(struct mddev *mdd
 	if (mddev_trylock(mddev)) {
 		int spares = 0;
 
+		if (mddev->safemode == 1)
+			mddev->safemode = 0;
+
 		if (mddev->ro) {
 			struct md_rdev *rdev;
 			if (!mddev->external && mddev->in_sync)

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/md-not-clear-safemode-for-external-metadata-array.patch queue-4.12/md-always-clear-safemode-when-md_check_recovery-gets-the-mddev-lock.patch queue-4.12/md-fix-test-in-md_write_start.patch