md: avoid taking the mutex on some ioctls.

Some ioctls don't need to take the mutex and doing so can cause
a delay as it is held during super-block update.
So move those ioctls out of the mutex and rely on rcu locking
to ensure we don't access stale data.

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

1 files changed, 62 insertions, 23 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 8e842b326ebd..feab588adb50 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -674,7 +674,18 @@ static struct md_rdev * find_rdev_nr(struct mddev *mddev, int nr)
         return NULL;
 }
 
-static struct md_rdev * find_rdev(struct mddev * mddev, dev_t dev)
+static struct md_rdev *find_rdev_nr_rcu(struct mddev *mddev, int nr)
+{
+        struct md_rdev *rdev;
+
+        rdev_for_each_rcu(rdev, mddev)
+                if (rdev->desc_nr == nr)
+                        return rdev;
+
+        return NULL;
+}
+
+static struct md_rdev *find_rdev(struct mddev *mddev, dev_t dev)
 {
         struct md_rdev *rdev;
 
@@ -685,6 +696,17 @@ static struct md_rdev * find_rdev(struct mddev * mddev, dev_t dev)
         return NULL;
 }
 
+static struct md_rdev *find_rdev_rcu(struct mddev *mddev, dev_t dev)
+{
+        struct md_rdev *rdev;
+
+        rdev_for_each_rcu(rdev, mddev)
+                if (rdev->bdev->bd_dev == dev)
+                        return rdev;
+
+        return NULL;
+}
+
 static struct md_personality *find_pers(int level, char *clevel)
 {
         struct md_personality *pers;
@@ -5509,8 +5531,9 @@ static int get_array_info(struct mddev * mddev, void __user * arg)
         int nr,working,insync,failed,spare;
         struct md_rdev *rdev;
 
-        nr=working=insync=failed=spare=0;
-        rdev_for_each(rdev, mddev) {
+        nr = working = insync = failed = spare = 0;
+        rcu_read_lock();
+        rdev_for_each_rcu(rdev, mddev) {
                 nr++;
                 if (test_bit(Faulty, &rdev->flags))
                         failed++;
@@ -5522,6 +5545,7 @@ static int get_array_info(struct mddev * mddev, void __user * arg)
                                 spare++;
                 }
         }
+        rcu_read_unlock();
 
         info.major_version = mddev->major_version;
         info.minor_version = mddev->minor_version;
@@ -5605,7 +5629,8 @@ static int get_disk_info(struct mddev * mddev, void __user * arg)
         if (copy_from_user(&info, arg, sizeof(info)))
                 return -EFAULT;
 
-        rdev = find_rdev_nr(mddev, info.number);
+        rcu_read_lock();
+        rdev = find_rdev_nr_rcu(mddev, info.number);
         if (rdev) {
                 info.major = MAJOR(rdev->bdev->bd_dev);
                 info.minor = MINOR(rdev->bdev->bd_dev);
@@ -5624,6 +5649,7 @@ static int get_disk_info(struct mddev * mddev, void __user * arg)
                 info.raid_disk = -1;
                 info.state = (1<<MD_DISK_REMOVED);
         }
+        rcu_read_unlock();
 
         if (copy_to_user(arg, &info, sizeof(info)))
                 return -EFAULT;
@@ -6232,18 +6258,22 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 static int set_disk_faulty(struct mddev *mddev, dev_t dev)
 {
         struct md_rdev *rdev;
+        int err = 0;
 
         if (mddev->pers == NULL)
                 return -ENODEV;
 
-        rdev = find_rdev(mddev, dev);
+        rcu_read_lock();
+        rdev = find_rdev_rcu(mddev, dev);
         if (!rdev)
-                return -ENODEV;
-
-        md_error(mddev, rdev);
-        if (!test_bit(Faulty, &rdev->flags))
-                return -EBUSY;
-        return 0;
+                err =  -ENODEV;
+        else {
+                md_error(mddev, rdev);
+                if (!test_bit(Faulty, &rdev->flags))
+                        err = -EBUSY;
+        }
+        rcu_read_unlock();
+        return err;
 }
 
 /*
@@ -6315,6 +6345,27 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
                 goto abort;
         }
 
+        /* Some actions do not requires the mutex */
+        switch (cmd) {
+        case GET_ARRAY_INFO:
+                if (!mddev->raid_disks && !mddev->external)
+                        err = -ENODEV;
+                else
+                        err = get_array_info(mddev, argp);
+                goto abort;
+
+        case GET_DISK_INFO:
+                if (!mddev->raid_disks && !mddev->external)
+                        err = -ENODEV;
+                else
+                        err = get_disk_info(mddev, argp);
+                goto abort;
+
+        case SET_DISK_FAULTY:
+                err = set_disk_faulty(mddev, new_decode_dev(arg));
+                goto abort;
+        }
+
         err = mddev_lock(mddev);
         if (err) {
                 printk(KERN_INFO 
@@ -6387,18 +6438,10 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
          */
         switch (cmd)
         {
-                case GET_ARRAY_INFO:
-                        err = get_array_info(mddev, argp);
-                        goto done_unlock;
-
                 case GET_BITMAP_FILE:
                         err = get_bitmap_file(mddev, argp);
                         goto done_unlock;
 
-                case GET_DISK_INFO:
-                        err = get_disk_info(mddev, argp);
-                        goto done_unlock;
-
                 case RESTART_ARRAY_RW:
                         err = restart_array(mddev);
                         goto done_unlock;
@@ -6480,10 +6523,6 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
                         err = hot_add_disk(mddev, new_decode_dev(arg));
                         goto done_unlock;
 
-                case SET_DISK_FAULTY:
-                        err = set_disk_faulty(mddev, new_decode_dev(arg));
-                        goto done_unlock;
-
                 case RUN_ARRAY:
                         err = do_md_run(mddev);
                         goto done_unlock;