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 (file)
--- 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);
        }