Patch "md: fix race when unfreezing sync_action" has been added to the 4.0-stable tree

Patch "md: fix race when unfreezing sync_action" has been added to the 4.0-stable tree

[gregkh]

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

    md: fix race when unfreezing sync_action

to the 4.0-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-fix-race-when-unfreezing-sync_action.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 56ccc1125bc141cf63927eda7febff4216dea2d3 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Thu, 28 May 2015 17:53:29 +1000
Subject: md: fix race when unfreezing sync_action

From: NeilBrown <neilb@suse.de>

commit 56ccc1125bc141cf63927eda7febff4216dea2d3 upstream.

A recent change removed the need for locking around writing
to "sync_action" (and various other places), but introduced a
subtle race.
When e.g. setting 'reshape' on a 'frozen' array, the 'frozen'
flag is cleared before 'reshape' is set, so the md thread can
get in and start trying recovery - which isn't wanted.

So instead of clearing MD_RECOVERY_FROZEN for any command
except 'frozen', only clear it when each specific command
is parsed.  This allows the handling of 'reshape' to clear
the bit while a lock is held.

Also remove some places where we set MD_RECOVERY_NEEDED,
as it is always set on non-error exit of the function.


Signed-off-by: NeilBrown <neilb@suse.de>
Fixes: 6791875e2e53 ("md: make reconfig_mutex optional for writes to md sysfs files.")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/md.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4138,12 +4138,12 @@ action_store(struct mddev *mddev, const
 	if (!mddev->pers || !mddev->pers->sync_request)
 		return -EINVAL;
 
-	if (cmd_match(page, "frozen"))
-		set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
-	else
-		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 
 	if (cmd_match(page, "idle") || cmd_match(page, "frozen")) {
+		if (cmd_match(page, "frozen"))
+			set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
+		else
+			clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 		flush_workqueue(md_misc_wq);
 		if (mddev->sync_thread) {
 			set_bit(MD_RECOVERY_INTR, &mddev->recovery);
@@ -4156,16 +4156,17 @@ action_store(struct mddev *mddev, const
 		   test_bit(MD_RECOVERY_NEEDED, &mddev->recovery))
 		return -EBUSY;
 	else if (cmd_match(page, "resync"))
-		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 	else if (cmd_match(page, "recover")) {
+		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 		set_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
-		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
 	} else if (cmd_match(page, "reshape")) {
 		int err;
 		if (mddev->pers->start_reshape == NULL)
 			return -EINVAL;
 		err = mddev_lock(mddev);
 		if (!err) {
+			clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 			err = mddev->pers->start_reshape(mddev);
 			mddev_unlock(mddev);
 		}
@@ -4177,6 +4178,7 @@ action_store(struct mddev *mddev, const
 			set_bit(MD_RECOVERY_CHECK, &mddev->recovery);
 		else if (!cmd_match(page, "repair"))
 			return -EINVAL;
+		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 		set_bit(MD_RECOVERY_REQUESTED, &mddev->recovery);
 		set_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 	}


Patches currently in stable-queue which might be from neilb@suse.de are

queue-4.0/md-raid5-don-t-record-new-size-if-resize_stripes-fails.patch
queue-4.0/md-raid0-fix-restore-to-sector-variable-in-raid0_make_request.patch
queue-4.0/md-fix-race-when-unfreezing-sync_action.patch
queue-4.0/sched-always-use-blk_schedule_flush_plug-in-io_schedule_out.patch