md: remove mddev_lock() from md_attr_show()

Most attributes can be read safely without any locking.
A race might lead to a slightly out-dated value, but nothing wrong.

We already have locking in some places where needed.
All that remains is can_clear_show(), behind_writes_used_show()
and action_show() which are easily fixed.

Signed-off-by: NeilBrown <neilb@suse.de>

2 files changed, 20 insertions, 16 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 3424b1915fc4..3a5767968ba0 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -2211,11 +2211,13 @@ __ATTR(metadata, S_IRUGO|S_IWUSR, metadata_show, metadata_store);
 static ssize_t can_clear_show(struct mddev *mddev, char *page)
 {
         int len;
+        spin_lock(&mddev->lock);
         if (mddev->bitmap)
                 len = sprintf(page, "%s\n", (mddev->bitmap->need_sync ?
                                              "false" : "true"));
         else
                 len = sprintf(page, "\n");
+        spin_unlock(&mddev->lock);
         return len;
 }
 
@@ -2240,10 +2242,15 @@ __ATTR(can_clear, S_IRUGO|S_IWUSR, can_clear_show, can_clear_store);
 static ssize_t
 behind_writes_used_show(struct mddev *mddev, char *page)
 {
+        ssize_t ret;
+        spin_lock(&mddev->lock);
         if (mddev->bitmap == NULL)
-                return sprintf(page, "0\n");
-        return sprintf(page, "%lu\n",
-                       mddev->bitmap->behind_writes_used);
+                ret = sprintf(page, "0\n");
+        else
+                ret = sprintf(page, "%lu\n",
+                              mddev->bitmap->behind_writes_used);
+        spin_unlock(&mddev->lock);
+        return ret;
 }
 
 static ssize_t
diff --git a/drivers/md/md.c b/drivers/md/md.c
index eb0c3b576d7d..dbbe5e6df24c 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4042,20 +4042,21 @@ static ssize_t
 action_show(struct mddev *mddev, char *page)
 {
         char *type = "idle";
-        if (test_bit(MD_RECOVERY_FROZEN, &mddev->recovery))
+        unsigned long recovery = mddev->recovery;
+        if (test_bit(MD_RECOVERY_FROZEN, &recovery))
                 type = "frozen";
-        else if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
-            (!mddev->ro && test_bit(MD_RECOVERY_NEEDED, &mddev->recovery))) {
-                if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
+        else if (test_bit(MD_RECOVERY_RUNNING, &recovery) ||
+            (!mddev->ro && test_bit(MD_RECOVERY_NEEDED, &recovery))) {
+                if (test_bit(MD_RECOVERY_RESHAPE, &recovery))
                         type = "reshape";
-                else if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
-                        if (!test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery))
+                else if (test_bit(MD_RECOVERY_SYNC, &recovery)) {
+                        if (!test_bit(MD_RECOVERY_REQUESTED, &recovery))
                                 type = "resync";
-                        else if (test_bit(MD_RECOVERY_CHECK, &mddev->recovery))
+                        else if (test_bit(MD_RECOVERY_CHECK, &recovery))
                                 type = "check";
                         else
                                 type = "repair";
-                } else if (test_bit(MD_RECOVERY_RECOVER, &mddev->recovery))
+                } else if (test_bit(MD_RECOVERY_RECOVER, &recovery))
                         type = "recover";
         }
         return sprintf(page, "%s\n", type);
@@ -4572,11 +4573,7 @@ md_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
         mddev_get(mddev);
         spin_unlock(&all_mddevs_lock);
 
-        rv = mddev_lock(mddev);
-        if (!rv) {
-                rv = entry->show(mddev, page);
-                mddev_unlock(mddev);
-        }
+        rv = entry->show(mddev, page);
         mddev_put(mddev);
         return rv;
 }