md: split mddev_find

commit 65aa97c4d2bfd76677c211b9d03ef05a98c6d68e upstream.

Split mddev_find into a simple mddev_find that just finds an existing
mddev by the unit number, and a more complicated mddev_find that deals
with find or allocating a mddev.

This turns out to fix this bug reported by Zhao Heming.

----------------------------- snip ------------------------------
commit d3374825ce57 ("md: make devices disappear when they are no longer
needed.") introduced protection between mddev creating & removing. The
md_open shouldn't create mddev when all_mddevs list doesn't contain
mddev. With currently code logic, there will be very easy to trigger
soft lockup in non-preempt env.

diff --git a/drivers/md/md.c b/drivers/md/md.c
index d602ce81e9e4c002fe3cc7eab27ed9b42d90e4b7..14ab9c293e3a0f67ba577bee6ed589041cc7eaad 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -753,6 +753,22 @@ void mddev_init(struct mddev *mddev)
 EXPORT_SYMBOL_GPL(mddev_init);
 
 static struct mddev *mddev_find(dev_t unit)
+{
+       struct mddev *mddev;
+
+       if (MAJOR(unit) != MD_MAJOR)
+               unit &= ~((1 << MdpMinorShift) - 1);
+
+       spin_lock(&all_mddevs_lock);
+       mddev = mddev_find_locked(unit);
+       if (mddev)
+               mddev_get(mddev);
+       spin_unlock(&all_mddevs_lock);
+
+       return mddev;
+}
+
+static struct mddev *mddev_find_or_alloc(dev_t unit)
 {
        struct mddev *mddev, *new = NULL;
 
@@ -5657,7 +5673,7 @@ static int md_alloc(dev_t dev, char *name)
         * writing to /sys/module/md_mod/parameters/new_array.
         */
        static DEFINE_MUTEX(disks_mutex);
-       struct mddev *mddev = mddev_find(dev);
+       struct mddev *mddev = mddev_find_or_alloc(dev);
        struct gendisk *disk;
        int partitioned;
        int shift;
@@ -6539,11 +6555,9 @@ static void autorun_devices(int part)
 
                md_probe(dev);
                mddev = mddev_find(dev);
-               if (!mddev || !mddev->gendisk) {
-                       if (mddev)
-                               mddev_put(mddev);
+               if (!mddev)
                        break;
-               }
+
                if (mddev_lock(mddev))
                        pr_warn("md: %s locked, cannot run\n", mdname(mddev));
                else if (mddev->raid_disks || mddev->major_version