Commit 56ccc112 authored by NeilBrown's avatar NeilBrown
Browse files

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: default avatarNeilBrown <neilb@suse.de>
Fixes: 6791875e ("md: make reconfig_mutex optional for writes to md sysfs files.")
parent 626f2092

drivers/md/md.c

+8 −6
Original line number Diff line number Diff line
@@ -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, "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);



	if (cmd_match(page, "idle") || cmd_match(page, "frozen")) {

		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);

	}

CRA Git | Maintained and supported by SUSTech CRA and CCSE