diff options
| -rw-r--r-- | module/zfs/zvol.c | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c index 7a448f194..d4d533f02 100644 --- a/module/zfs/zvol.c +++ b/module/zfs/zvol.c @@ -891,11 +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); |