svn commit: r354892 - head/sys/kern

[Mateusz Guzik]

Author: mjg
Date: Wed Nov 20 12:07:54 2019
New Revision: 354892
URL: https://svnweb.freebsd.org/changeset/base/354892

Log:
  vfs: perform a more racy check in vfs_notify_upper
  
  Locking mp does not buy anything interms of correctness and only contributes to
  contention.

Modified:
  head/sys/kern/vfs_subr.c

Modified: head/sys/kern/vfs_subr.c
==============================================================================
--- head/sys/kern/vfs_subr.c	Wed Nov 20 12:06:29 2019	(r354891)
+++ head/sys/kern/vfs_subr.c	Wed Nov 20 12:07:54 2019	(r354892)
@@ -3526,11 +3526,9 @@ vfs_notify_upper(struct vnode *vp, int event)
 	mp = vp->v_mount;
 	if (mp == NULL)
 		return;
-
-	MNT_ILOCK(mp);
 	if (TAILQ_EMPTY(&mp->mnt_uppers))
-		goto unlock;
-	MNT_IUNLOCK(mp);
+		return;
+
 	mmp = malloc(sizeof(struct mount), M_TEMP, M_WAITOK | M_ZERO);
 	mmp->mnt_op = &vgonel_vfsops;
 	mmp->mnt_kern_flag |= MNTK_MARKER;
@@ -3564,7 +3562,6 @@ vfs_notify_upper(struct vnode *vp, int event)
 		mp->mnt_kern_flag &= ~MNTK_VGONE_WAITER;
 		wakeup(&mp->mnt_uppers);
 	}
-unlock:
 	MNT_IUNLOCK(mp);
 }