md: protect ->pers changes with mddev->lock

->pers is already protected by ->reconfig_mutex, and
cannot possibly change when there are threads running or
outstanding IO.

However there are some places where we access ->pers
not in a thread or IO context, and where ->reconfig_mutex
is unnecessarily heavy-weight:  level_show and md_seq_show().

So protect all changes, and those accesses, with ->lock.
This is a step toward taking those accesses out from under
reconfig_mutex.

[Fixed missing "mddev->pers" -> "pers" conversion, thanks to
 Dan Carpenter <dan.carpenter@oracle.com>]

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

2 files changed, 35 insertions, 21 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 58f531f8dcc2..4db4e4146a35 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3264,15 +3264,20 @@ __ATTR(safe_mode_delay, S_IRUGO|S_IWUSR,safe_delay_show, safe_delay_store);
 static ssize_t
 level_show(struct mddev *mddev, char *page)
 {
-        struct md_personality *p = mddev->pers;
+        struct md_personality *p;
+        int ret;
+        spin_lock(&mddev->lock);
+        p = mddev->pers;
         if (p)
-                return sprintf(page, "%s\n", p->name);
+                ret = sprintf(page, "%s\n", p->name);
         else if (mddev->clevel[0])
-                return sprintf(page, "%s\n", mddev->clevel);
+                ret = sprintf(page, "%s\n", mddev->clevel);
         else if (mddev->level != LEVEL_NONE)
-                return sprintf(page, "%d\n", mddev->level);
+                ret = sprintf(page, "%d\n", mddev->level);
         else
-                return 0;
+                ret = 0;
+        spin_unlock(&mddev->lock);
+        return ret;
 }
 
 static ssize_t
@@ -3374,6 +3379,8 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
         /* Looks like we have a winner */
         mddev_suspend(mddev);
         mddev_detach(mddev);
+
+        spin_lock(&mddev->lock);
         oldpers = mddev->pers;
         oldpriv = mddev->private;
         mddev->pers = pers;
@@ -3385,6 +3392,7 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
         mddev->delta_disks = 0;
         mddev->reshape_backwards = 0;
         mddev->degraded = 0;
+        spin_unlock(&mddev->lock);
 
         if (oldpers->sync_request == NULL &&
             mddev->external) {
@@ -4866,7 +4874,6 @@ int md_run(struct mddev *mddev)
                                mddev->clevel);
                 return -EINVAL;
         }
-        mddev->pers = pers;
         spin_unlock(&pers_lock);
         if (mddev->level != pers->level) {
                 mddev->level = pers->level;
@@ -4877,7 +4884,6 @@ int md_run(struct mddev *mddev)
         if (mddev->reshape_position != MaxSector &&
             pers->start_reshape == NULL) {
                 /* This personality cannot handle reshaping... */
-                mddev->pers = NULL;
                 module_put(pers->owner);
                 return -EINVAL;
         }
@@ -4921,19 +4927,19 @@ int md_run(struct mddev *mddev)
         if (start_readonly && mddev->ro == 0)
                 mddev->ro = 2; /* read-only, but switch on first write */
 
-        err = mddev->pers->run(mddev);
+        err = pers->run(mddev);
         if (err)
                 printk(KERN_ERR "md: pers->run() failed ...\n");
-        else if (mddev->pers->size(mddev, 0, 0) < mddev->array_sectors) {
+        else if (pers->size(mddev, 0, 0) < mddev->array_sectors) {
                 WARN_ONCE(!mddev->external_size, "%s: default size too small,"
                           " but 'external_size' not in effect?\n", __func__);
                 printk(KERN_ERR
                        "md: invalid array_size %llu > default size %llu\n",
                        (unsigned long long)mddev->array_sectors / 2,
-                       (unsigned long long)mddev->pers->size(mddev, 0, 0) / 2);
+                       (unsigned long long)pers->size(mddev, 0, 0) / 2);
                 err = -EINVAL;
         }
-        if (err == 0 && mddev->pers->sync_request &&
+        if (err == 0 && pers->sync_request &&
             (mddev->bitmap_info.file || mddev->bitmap_info.offset)) {
                 err = bitmap_create(mddev);
                 if (err)
@@ -4942,9 +4948,8 @@ int md_run(struct mddev *mddev)
         }
         if (err) {
                 mddev_detach(mddev);
-                mddev->pers->free(mddev, mddev->private);
-                module_put(mddev->pers->owner);
-                mddev->pers = NULL;
+                pers->free(mddev, mddev->private);
+                module_put(pers->owner);
                 bitmap_destroy(mddev);
                 return err;
         }
@@ -4953,7 +4958,7 @@ int md_run(struct mddev *mddev)
                 mddev->queue->backing_dev_info.congested_fn = md_congested;
                 blk_queue_merge_bvec(mddev->queue, md_mergeable_bvec);
         }
-        if (mddev->pers->sync_request) {
+        if (pers->sync_request) {
                 if (mddev->kobj.sd &&
                     sysfs_create_group(&mddev->kobj, &md_redundancy_group))
                         printk(KERN_WARNING
@@ -4972,7 +4977,10 @@ int md_run(struct mddev *mddev)
         mddev->safemode_delay = (200 * HZ)/1000 +1; /* 200 msec delay */
         mddev->in_sync = 1;
         smp_wmb();
+        spin_lock(&mddev->lock);
+        mddev->pers = pers;
         mddev->ready = 1;
+        spin_unlock(&mddev->lock);
         rdev_for_each(rdev, mddev)
                 if (rdev->raid_disk >= 0)
                         if (sysfs_link_rdev(mddev, rdev))
@@ -5126,7 +5134,7 @@ static void mddev_detach(struct mddev *mddev)
                 wait_event(bitmap->behind_wait,
                            atomic_read(&bitmap->behind_writes) == 0);
         }
-        if (mddev->pers->quiesce) {
+        if (mddev->pers && mddev->pers->quiesce) {
                 mddev->pers->quiesce(mddev, 1);
                 mddev->pers->quiesce(mddev, 0);
         }
@@ -5137,13 +5145,16 @@ static void mddev_detach(struct mddev *mddev)
 
 static void __md_stop(struct mddev *mddev)
 {
-        mddev->ready = 0;
+        struct md_personality *pers = mddev->pers;
         mddev_detach(mddev);
-        mddev->pers->free(mddev, mddev->private);
-        if (mddev->pers->sync_request && mddev->to_remove == NULL)
-                mddev->to_remove = &md_redundancy_group;
-        module_put(mddev->pers->owner);
+        spin_lock(&mddev->lock);
+        mddev->ready = 0;
         mddev->pers = NULL;
+        spin_unlock(&mddev->lock);
+        pers->free(mddev, mddev->private);
+        if (pers->sync_request && mddev->to_remove == NULL)
+                mddev->to_remove = &md_redundancy_group;
+        module_put(pers->owner);
         clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 }
 
@@ -6942,6 +6953,7 @@ static int md_seq_show(struct seq_file *seq, void *v)
         if (mddev_lock(mddev) < 0)
                 return -EINTR;
 
+        spin_lock(&mddev->lock);
         if (mddev->pers || mddev->raid_disks || !list_empty(&mddev->disks)) {
                 seq_printf(seq, "%s : %sactive", mdname(mddev),
                                                 mddev->pers ? "" : "in");
@@ -7012,6 +7024,7 @@ static int md_seq_show(struct seq_file *seq, void *v)
 
                 seq_printf(seq, "\n");
         }
+        spin_unlock(&mddev->lock);
         mddev_unlock(mddev);
 
         return 0;
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 37e7c17e56a6..e41559dccdc9 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -391,6 +391,7 @@ struct mddev {
          *   rdev superblocks, events
          *   clearing MD_CHANGE_*
          *   in_sync - and related safemode and MD_CHANGE changes
+         *   pers (also protected by reconfig_mutex and pending IO).
          */
         spinlock_t                      lock;
         wait_queue_head_t               sb_wait;        /* for waiting on superblock updates */