X-Git-Url: https://git.camperquake.de/gitweb.cgi?a=blobdiff_plain;f=module%2Fzfs%2Fzvol.c;h=c6cfac26d4afbb2e42576f87f77023abc32e8485;hb=36f86f73f68548f46eb3229c8adf583d59fa9988;hp=c3bd25c3b610be4ea1a63f7ade350fa51bbedc12;hpb=7bd04f2d7d99780f190d4027e6e81fc0df11ba95;p=zfs.git

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index c3bd25c..c6cfac2 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -141,6 +141,29 @@ zvol_find_by_name(const char *name)
 	return NULL;
 }
 
+
+/*
+ * Given a path, return TRUE if path is a ZVOL.
+ */
+boolean_t
+zvol_is_zvol(const char *device)
+{
+	struct block_device *bdev;
+	unsigned int major;
+
+	bdev = lookup_bdev(device);
+	if (IS_ERR(bdev))
+		return (B_FALSE);
+
+	major = MAJOR(bdev->bd_dev);
+	bdput(bdev);
+
+	if (major == zvol_major)
+            return (B_TRUE);
+
+	return (B_FALSE);
+}
+
 /*
  * ZFS_IOC_CREATE callback handles dmu zvol and zap object creation.
  */
@@ -868,25 +891,49 @@ zvol_first_open(zvol_state_t *zv)
 {
 	objset_t *os;
 	uint64_t volsize;
+	int locked = 0;
 	int error;
 	uint64_t ro;
 
+	/*
+	 * In all other cases the spa_namespace_lock is taken before the
+	 * bdev->bd_mutex lock.  But in this case the Linux __blkdev_get()
+	 * function calls fops->open() with the bdev->bd_mutex lock held.
+	 *
+	 * To avoid a potential lock inversion deadlock we preemptively
+	 * try to take the spa_namespace_lock().  Normally it will not
+	 * be contended and this is safe because spa_open_common() handles
+	 * the case where the caller already holds the spa_namespace_lock.
+	 *
+	 * When it is contended we risk a lock inversion if we were to
+	 * block waiting for the lock.  Luckily, the __blkdev_get()
+	 * function allows us to return -ERESTARTSYS which will result in
+	 * bdev->bd_mutex being dropped, reacquired, and fops->open() being
+	 * called again.  This process can be repeated safely until both
+	 * locks are acquired.
+	 */
+	if (!mutex_owned(&spa_namespace_lock)) {
+		locked = mutex_tryenter(&spa_namespace_lock);
+		if (!locked)
+			return (-ERESTARTSYS);
+	}
+
 	/* lie and say we're read-only */
 	error = dmu_objset_own(zv->zv_name, DMU_OST_ZVOL, 1, zvol_tag, &os);
 	if (error)
-		return (-error);
+		goto out_mutex;
 
 	error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize);
 	if (error) {
-	        dmu_objset_disown(os, zvol_tag);
-	        return (-error);
+		dmu_objset_disown(os, zvol_tag);
+		goto out_mutex;
 	}
 
 	zv->zv_objset = os;
 	error = dmu_bonus_hold(os, ZVOL_OBJ, zvol_tag, &zv->zv_dbuf);
 	if (error) {
-	        dmu_objset_disown(os, zvol_tag);
-	        return (-error);
+		dmu_objset_disown(os, zvol_tag);
+		goto out_mutex;
 	}
 
 	set_capacity(zv->zv_disk, volsize >> 9);
@@ -895,13 +942,17 @@ zvol_first_open(zvol_state_t *zv)
 
 	VERIFY(dsl_prop_get_integer(zv->zv_name, "readonly", &ro, NULL) == 0);
 	if (ro || dmu_objset_is_snapshot(os)) {
-                set_disk_ro(zv->zv_disk, 1);
-	        zv->zv_flags |= ZVOL_RDONLY;
+		set_disk_ro(zv->zv_disk, 1);
+		zv->zv_flags |= ZVOL_RDONLY;
 	} else {
-                set_disk_ro(zv->zv_disk, 0);
-	        zv->zv_flags &= ~ZVOL_RDONLY;
+		set_disk_ro(zv->zv_disk, 0);
+		zv->zv_flags &= ~ZVOL_RDONLY;
 	}
 
+out_mutex:
+	if (locked)
+		mutex_exit(&spa_namespace_lock);
+
 	return (-error);
 }
 
@@ -1306,9 +1357,9 @@ __zvol_create_minor(const char *name)
 	else
 		zil_replay(os, zv, zvol_replay_vector);
 
+	zv->zv_objset = NULL;
 out_dmu_objset_disown:
 	dmu_objset_disown(os, zvol_tag);
-	zv->zv_objset = NULL;
 out_doi:
 	kmem_free(doi, sizeof(dmu_object_info_t));
 out: