[src/trunk]: src/sys/kern Restructure vdrain_vrele(). While it is not possib...

[hannken <hannken%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/7157ce0b27b0
branches:  trunk
changeset: 349722:7157ce0b27b0
user:      hannken <hannken%NetBSD.org@localhost>
date:      Tue Dec 20 10:02:21 2016 +0000

description:
Restructure vdrain_vrele().  While it is not possible for another thread
to lock this vnodes v_interlock -> vdrain_lock another vnode sharing the
v_interlock may lock this order.
While here, restore fstrans_start_nowait arg to FSTRANS_LAZY.

Fixes a deadlock seen recently on some pbulk environments.

diffstat:

 sys/kern/vfs_vnode.c |  25 ++++++++++++-------------
 1 files changed, 12 insertions(+), 13 deletions(-)

diffs (55 lines):

diff -r ea2abdc43a96 -r 7157ce0b27b0 sys/kern/vfs_vnode.c
--- a/sys/kern/vfs_vnode.c      Tue Dec 20 09:22:18 2016 +0000
+++ b/sys/kern/vfs_vnode.c      Tue Dec 20 10:02:21 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_vnode.c,v 1.63 2016/12/14 15:49:35 hannken Exp $   */
+/*     $NetBSD: vfs_vnode.c,v 1.64 2016/12/20 10:02:21 hannken Exp $   */
 
 /*-
  * Copyright (c) 1997-2011 The NetBSD Foundation, Inc.
@@ -156,7 +156,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.63 2016/12/14 15:49:35 hannken Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.64 2016/12/20 10:02:21 hannken Exp $");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
@@ -502,26 +502,25 @@
 
        KASSERT(mutex_owned(&vdrain_lock));
 
+       mp = vp->v_mount;
+       if (fstrans_start_nowait(mp, FSTRANS_LAZY) != 0)
+               return;
+
        /*
-        * Safe to take v_interlock -- no other thread will
-        * lock v_interlock -> vdrain_lock as usecount > 0.
+        * First remove the vnode from the vrele list.
+        * Put it on the last lru list, the last vrele()
+        * will put it back onto the right list before
+        * its v_usecount reaches zero.
         */
-       mutex_enter(vp->v_interlock);
-       mp = vp->v_mount;
-       if (fstrans_start_nowait(mp, FSTRANS_SHARED) != 0) {
-               mutex_exit(vp->v_interlock);
-               return;
-       }
-
-       /* First put the vnode back onto its lru list. */
        KASSERT(node->vi_lrulisthd == &lru_vrele_list);
        TAILQ_REMOVE(node->vi_lrulisthd, node, vi_lrulist);
-       node->vi_lrulisthd = lru_which(vp);
+       node->vi_lrulisthd = &lru_hold_list;
        TAILQ_INSERT_TAIL(node->vi_lrulisthd, node, vi_lrulist);
 
        vdrain_retry = true;
        mutex_exit(&vdrain_lock);
 
+       mutex_enter(vp->v_interlock);
        vrelel(vp, 0);
        fstrans_done(mp);