[PATCH] md: avoid a deadlock when removing a device from an md array via sysfs

A device can be removed from an md array via e.g.
  echo remove > /sys/block/md3/md/dev-sde/state

This will try to remove the 'dev-sde' subtree which will deadlock
since
  commit e7b0d26a86943370c04d6833c6edba2a72a6e240

With this patch we run the kobject_del via schedule_work so as to
avoid the deadlock.

Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 2a9b6a0..509171c 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1378,6 +1378,12 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
        return err;
 }
 
+static void delayed_delete(struct work_struct *ws)
+{
+       mdk_rdev_t *rdev = container_of(ws, mdk_rdev_t, del_work);
+       kobject_del(&rdev->kobj);
+}
+
 static void unbind_rdev_from_array(mdk_rdev_t * rdev)
 {
        char b[BDEVNAME_SIZE];
@@ -1390,7 +1396,12 @@ static void unbind_rdev_from_array(mdk_rdev_t * rdev)
        printk(KERN_INFO "md: unbind<%s>\n", bdevname(rdev->bdev,b));
        rdev->mddev = NULL;
        sysfs_remove_link(&rdev->kobj, "block");
-       kobject_del(&rdev->kobj);
+
+       /* We need to delay this, otherwise we can deadlock when
+        * writing to 'remove' to "dev/state"
+        */
+       INIT_WORK(&rdev->del_work, delayed_delete);
+       schedule_work(&rdev->del_work);
 }
 
 /*
@@ -3389,6 +3400,9 @@ static int do_md_stop(mddev_t * mddev, int mode)
                                sysfs_remove_link(&mddev->kobj, nm);
                        }
 
+               /* make sure all delayed_delete calls have finished */
+               flush_scheduled_work();
+
                export_array(mddev);
 
                mddev->array_size = 0;

diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 8245c28..de72c49 100644 (file)
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -104,6 +104,7 @@ struct mdk_rdev_s
                                           * for reporting to userspace and storing
                                           * in superblock.
                                           */
+       struct work_struct del_work;    /* used for delayed sysfs removal */
 };
 
 struct mddev_s