Check for RW_WRITE_HELD in zfs_inactive

Before read locking z_teardown_inactive_lock, we need to check if we have
already had write lock on it. Otherwise, we would deadlock on ourself when
doing rollback:

zfs_ioc_rollback
->zfs_suspend_fs (z_teardown_inactive_lock, RW_WRITER)
->zfs_resume_fs->zfs_rezget->zfs_iput_async->iput-> ...
  ->zfs_inactive (z_teardown_inactive_lock, RW_READER)

Signed-off-by: Chunwei Chen <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2869

1 files changed, 10 insertions, 3 deletions

diff --git a/module/zfs/zfs_vnops.c b/module/zfs/zfs_vnops.c
index 2292ff652..53d02a3aa 100644
--- a/module/zfs/zfs_vnops.c
+++ b/module/zfs/zfs_vnops.c
@@ -4096,10 +4096,16 @@ zfs_inactive(struct inode *ip)
 	znode_t	*zp = ITOZ(ip);
 	zfs_sb_t *zsb = ITOZSB(ip);
 	int error;
+	int need_unlock = 0;
 
-	rw_enter(&zsb->z_teardown_inactive_lock, RW_READER);
+	/* Only read lock if we haven't already write locked, e.g. rollback */
+	if (!RW_WRITE_HELD(&zsb->z_teardown_inactive_lock)) {
+		need_unlock = 1;
+		rw_enter(&zsb->z_teardown_inactive_lock, RW_READER);
+	}
 	if (zp->z_sa_hdl == NULL) {
-		rw_exit(&zsb->z_teardown_inactive_lock);
+		if (need_unlock)
+			rw_exit(&zsb->z_teardown_inactive_lock);
 		return;
 	}
 
@@ -4122,7 +4128,8 @@ zfs_inactive(struct inode *ip)
 	}
 
 	zfs_zinactive(zp);
-	rw_exit(&zsb->z_teardown_inactive_lock);
+	if (need_unlock)
+		rw_exit(&zsb->z_teardown_inactive_lock);
 }
 EXPORT_SYMBOL(zfs_inactive);