X-Git-Url: https://git.camperquake.de/gitweb.cgi?a=blobdiff_plain;f=module%2Fzfs%2Fzvol.c;h=d4d533f0231d0560092921d033d968cba38ebe09;hb=91579709fccd3e55a21970742b66c388fb1403db;hp=5d4802560201cb839ac662a8927d6380f8958b0c;hpb=f74a147c022f79916e8525c2c16b1603f91202aa;p=zfs.git

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 5d48025..d4d533f 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.
  */
@@ -868,11 +891,39 @@ 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 (locked)
+		mutex_exit(&spa_namespace_lock);
+
 	if (error)
 		return (-error);