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Date:      Sat, 9 Nov 2013 20:30:14 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r257898 - in head/sys: kern sys
Message-ID:  <201311092030.rA9KUEtl027202@svn.freebsd.org>
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Author: kib
Date: Sat Nov  9 20:30:13 2013
New Revision: 257898
URL: http://svnweb.freebsd.org/changeset/base/257898

Log:
  Both vn_close() and VFS_PROLOGUE() evaluate vp->v_mount twice, without
  holding the vnode lock; vp->v_mount is checked first for NULL
  equiality, and then dereferenced if not NULL.  If vnode is reclaimed
  meantime, second dereference would still give NULL.  Change
  VFS_PROLOGUE() to evaluate the mp once, convert MNTK_SHARED_WRITES and
  MNTK_EXTENDED_SHARED tests into inline functions.
  
  Reviewed by:	alc
  Tested by:	pho
  Sponsored by:	The FreeBSD Foundation
  MFC after:	2 weeks

Modified:
  head/sys/kern/vfs_lookup.c
  head/sys/kern/vfs_vnops.c
  head/sys/sys/mount.h

Modified: head/sys/kern/vfs_lookup.c
==============================================================================
--- head/sys/kern/vfs_lookup.c	Sat Nov  9 20:11:21 2013	(r257897)
+++ head/sys/kern/vfs_lookup.c	Sat Nov  9 20:30:13 2013	(r257898)
@@ -424,13 +424,8 @@ needs_exclusive_leaf(struct mount *mp, i
 	 * extended shared operations, then use a shared lock for the
 	 * leaf node, otherwise use an exclusive lock.
 	 */
-	if (flags & ISOPEN) {
-		if (mp != NULL &&
-		    (mp->mnt_kern_flag & MNTK_EXTENDED_SHARED))
-			return (0);
-		else
-			return (1);
-	}
+	if ((flags & ISOPEN) != 0)
+		return (!MNT_EXTENDED_SHARED(mp));
 
 	/*
 	 * Lookup requests outside of open() that specify LOCKSHARED

Modified: head/sys/kern/vfs_vnops.c
==============================================================================
--- head/sys/kern/vfs_vnops.c	Sat Nov  9 20:11:21 2013	(r257897)
+++ head/sys/kern/vfs_vnops.c	Sat Nov  9 20:30:13 2013	(r257898)
@@ -360,8 +360,8 @@ vn_close(vp, flags, file_cred, td)
 	struct mount *mp;
 	int error, lock_flags;
 
-	if (vp->v_type != VFIFO && !(flags & FWRITE) && vp->v_mount != NULL &&
-	    vp->v_mount->mnt_kern_flag & MNTK_EXTENDED_SHARED)
+	if (vp->v_type != VFIFO && (flags & FWRITE) == 0 &&
+	    MNT_EXTENDED_SHARED(vp->v_mount))
 		lock_flags = LK_SHARED;
 	else
 		lock_flags = LK_EXCLUSIVE;

Modified: head/sys/sys/mount.h
==============================================================================
--- head/sys/sys/mount.h	Sat Nov  9 20:11:21 2013	(r257897)
+++ head/sys/sys/mount.h	Sat Nov  9 20:30:13 2013	(r257898)
@@ -362,8 +362,19 @@ void          __mnt_vnode_markerfree_act
 #define MNTK_LOOKUP_SHARED	0x40000000 /* FS supports shared lock lookups */
 #define	MNTK_NOKNOTE	0x80000000	/* Don't send KNOTEs from VOP hooks */
 
-#define	MNT_SHARED_WRITES(mp) (((mp) != NULL) && 	\
-				((mp)->mnt_kern_flag & MNTK_SHARED_WRITES))
+static inline int
+MNT_SHARED_WRITES(struct mount *mp)
+{
+
+	return (mp != NULL && (mp->mnt_kern_flag & MNTK_SHARED_WRITES) != 0);
+}
+
+static inline int
+MNT_EXTENDED_SHARED(struct mount *mp)
+{
+
+	return (mp != NULL && (mp->mnt_kern_flag & MNTK_EXTENDED_SHARED) != 0);
+}
 
 /*
  * Sysctl CTL_VFS definitions.
@@ -636,10 +647,12 @@ struct vfsops {
 vfs_statfs_t	__vfs_statfs;
 
 #define	VFS_PROLOGUE(MP)	do {					\
+	struct mount *mp__;						\
 	int _enable_stops;						\
 									\
-	_enable_stops = ((MP) != NULL &&				\
-	    ((MP)->mnt_vfc->vfc_flags & VFCF_SBDRY) && sigdeferstop())
+	mp__ = (MP);							\
+	_enable_stops = (mp__ != NULL &&				\
+	    (mp__->mnt_vfc->vfc_flags & VFCF_SBDRY) && sigdeferstop())
 
 #define	VFS_EPILOGUE(MP)						\
 	if (_enable_stops)						\

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