Skip to contentSkip to conversation

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

PATCH [email protected] 1 participant 1 message Jun 3, 2015

Subsystems (2)
Stable branch MD RAID
lore
Share & tools
lore

[email protected]

author maintainer Applied
#0 lore raw

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 <[email protected]> know about it.

Quoted 1 line

From 56ccc1125bc141cf63927eda7febff4216dea2d3 Mon Sep 17 00:00:00 2001

From: NeilBrown <[email protected]>
Date: Thu, 28 May 2015 17:53:29 +1000
Subject: md: fix race when unfreezing sync_action

From: NeilBrown <[email protected]>

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 <[email protected]>
Fixes 6791875e2e53 ("md: make reconfig_mutex optional for writes to md sysfs files.")
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 drivers/md/md.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)
drivers/md/md.c +8 -6
@@ -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 [email protected] 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