From: NeilBrown <neilb@suse.de>
Date: Thu, 28 May 2015 07:53:29 +0000 (+1000)
Subject: md: fix race when unfreezing sync_action
X-Git-Tag: v5.15~15720^2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=56ccc1125bc141cf63927eda7febff4216dea2d3;p=platform%2Fkernel%2Flinux-starfive.git

md: fix race when unfreezing sync_action

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.")
---

diff --git a/drivers/md/md.c b/drivers/md/md.c
index d4f31e1..8f10f4e 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4211,12 +4211,12 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 	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);
@@ -4229,16 +4229,17 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 		   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);
 		}
@@ -4250,6 +4251,7 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 			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);
 	}