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Date:      Sun, 6 Oct 2013 06:09:43 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org
Subject:   svn commit: r256077 - stable/9/sys/kern
Message-ID:  <201310060609.r9669hQM028286@svn.freebsd.org>
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Author: kib
Date: Sun Oct  6 06:09:43 2013
New Revision: 256077
URL: http://svnweb.freebsd.org/changeset/base/256077

Log:
  MFC r255941:
  Increase the chance of the buffer write from the bufdaemon helper
  context to succeed. If the locked vnode which owns the buffer to be
  written is shared locked, try the non-blocking upgrade of the lock to
  exclusive.

Modified:
  stable/9/sys/kern/vfs_bio.c
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/9/sys/kern/vfs_bio.c
==============================================================================
--- stable/9/sys/kern/vfs_bio.c	Sun Oct  6 06:05:11 2013	(r256076)
+++ stable/9/sys/kern/vfs_bio.c	Sun Oct  6 06:09:43 2013	(r256077)
@@ -2671,6 +2671,8 @@ flushbufqueues(struct vnode *lvp, int qu
 	int hasdeps;
 	int flushed;
 	int target;
+	int error;
+	bool unlock;
 
 	if (lvp == NULL) {
 		target = numdirtybuffers - lodirtybuffers;
@@ -2751,7 +2753,16 @@ flushbufqueues(struct vnode *lvp, int qu
 			BUF_UNLOCK(bp);
 			continue;
 		}
-		if (vn_lock(vp, LK_EXCLUSIVE | LK_NOWAIT | LK_CANRECURSE) == 0) {
+		if (lvp == NULL) {
+			unlock = true;
+			error = vn_lock(vp, LK_EXCLUSIVE | LK_NOWAIT);
+		} else {
+			ASSERT_VOP_LOCKED(vp, "getbuf");
+			unlock = false;
+			error = VOP_ISLOCKED(vp) == LK_EXCLUSIVE ? 0 :
+			    vn_lock(vp, LK_TRYUPGRADE);
+		}
+		if (error == 0) {
 			mtx_unlock(&bqlock);
 			CTR3(KTR_BUF, "flushbufqueue(%p) vp %p flags %X",
 			    bp, bp->b_vp, bp->b_flags);
@@ -2763,7 +2774,8 @@ flushbufqueues(struct vnode *lvp, int qu
 				notbufdflashes++;
 			}
 			vn_finished_write(mp);
-			VOP_UNLOCK(vp, 0);
+			if (unlock)
+				VOP_UNLOCK(vp, 0);
 			flushwithdeps += hasdeps;
 			flushed++;

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