From 2ff47c5f181b6ccf2ad64d3552687e28781eab5a Mon Sep 17 00:00:00 2001
From: John Baldwin <jhb@FreeBSD.org>
Date: Tue, 4 Nov 2008 19:04:01 +0000
Subject: [PATCH] Remove unnecessary locking around vn_fullpath().  The vnode
 lock for the vnode in question does not need to be held.  All the data
 structures used during the name lookup are protected by the global name cache
 lock. Instead, the caller merely needs to ensure a reference is held on the
 vnode (such as vhold()) to keep it from being freed.

In the case of procfs' <pid>/file entry, grab the process lock while we
gain a new reference (via vhold()) on p_textvp to fully close races with
execve(2).

For the kern.proc.vmmap sysctl handler, use a shared vnode lock around
the call to VOP_GETATTR() rather than an exclusive lock.

MFC after:	1 month
---
 sys/dev/hwpmc/hwpmc_mod.c  |  2 --
 sys/fs/procfs/procfs.c     | 12 ++++--------
 sys/fs/procfs/procfs_map.c |  5 ++---
 sys/kern/kern_descrip.c    | 10 ++++------
 sys/kern/kern_proc.c       |  4 ++--
 5 files changed, 12 insertions(+), 21 deletions(-)

diff --git a/sys/dev/hwpmc/hwpmc_mod.c b/sys/dev/hwpmc/hwpmc_mod.c
index f750d46e409..61c07350d4a 100644
--- a/sys/dev/hwpmc/hwpmc_mod.c
+++ b/sys/dev/hwpmc/hwpmc_mod.c
@@ -680,9 +680,7 @@ pmc_getfilename(struct vnode *v, char **fullpath, char **freepath)
 
 	*fullpath = "unknown";
 	*freepath = NULL;
-	vn_lock(v, LK_CANRECURSE | LK_EXCLUSIVE | LK_RETRY);
 	vn_fullpath(curthread, v, fullpath, freepath);
-	VOP_UNLOCK(v, 0);
 }
 
 /*
diff --git a/sys/fs/procfs/procfs.c b/sys/fs/procfs/procfs.c
index bc0efdaa2f6..26bd18532f8 100644
--- a/sys/fs/procfs/procfs.c
+++ b/sys/fs/procfs/procfs.c
@@ -70,17 +70,13 @@ procfs_doprocfile(PFS_FILL_ARGS)
 	char *fullpath = "unknown";
 	char *freepath = NULL;
 	struct vnode *textvp;
-	int err;
 
+	PROC_LOCK(p);
 	textvp = p->p_textvp;
-	VI_LOCK(textvp);
-	vholdl(textvp);
-	err = vn_lock(textvp, LK_EXCLUSIVE | LK_INTERLOCK);
-	vdrop(textvp);
-	if (err)
-		return (err);
+	vhold(textvp);
+	PROC_UNLOCK(p);
 	vn_fullpath(td, textvp, &fullpath, &freepath);
-	VOP_UNLOCK(textvp, 0);
+	vdrop(textvp);
 	sbuf_printf(sb, "%s", fullpath);
 	if (freepath)
 		free(freepath, M_TEMP);
diff --git a/sys/fs/procfs/procfs_map.c b/sys/fs/procfs/procfs_map.c
index 1a9e4aaa8b8..0c671b4c286 100644
--- a/sys/fs/procfs/procfs_map.c
+++ b/sys/fs/procfs/procfs_map.c
@@ -175,10 +175,9 @@ procfs_doprocmap(PFS_FILL_ARGS)
 			shadow_count = obj->shadow_count;
 			VM_OBJECT_UNLOCK(obj);
 			if (vp != NULL) {
-				vfslocked = VFS_LOCK_GIANT(vp->v_mount);
-				vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 				vn_fullpath(td, vp, &fullpath, &freepath);
-				vput(vp);
+				vfslocked = VFS_LOCK_GIANT(vp->v_mount);
+				vrele(vp);
 				VFS_UNLOCK_GIANT(vfslocked);
 			}
 		} else {
diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index df92aca1fdf..833aa2c4e04 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -2537,10 +2537,9 @@ export_vnode_for_sysctl(struct vnode *vp, int type,
 	freepath = NULL;
 	fullpath = "-";
 	FILEDESC_SUNLOCK(fdp);
-	vfslocked = VFS_LOCK_GIANT(vp->v_mount);
-	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 	vn_fullpath(curthread, vp, &fullpath, &freepath);
-	vput(vp);
+	vfslocked = VFS_LOCK_GIANT(vp->v_mount);
+	vrele(vp);
 	VFS_UNLOCK_GIANT(vfslocked);
 	strlcpy(kif->kf_path, fullpath, sizeof(kif->kf_path));
 	if (freepath != NULL)
@@ -2708,10 +2707,9 @@ sysctl_kern_proc_filedesc(SYSCTL_HANDLER_ARGS)
 			freepath = NULL;
 			fullpath = "-";
 			FILEDESC_SUNLOCK(fdp);
-			vfslocked = VFS_LOCK_GIANT(vp->v_mount);
-			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 			vn_fullpath(curthread, vp, &fullpath, &freepath);
-			vput(vp);
+			vfslocked = VFS_LOCK_GIANT(vp->v_mount);
+			vrele(vp);
 			VFS_UNLOCK_GIANT(vfslocked);
 			strlcpy(kif->kf_path, fullpath,
 			    sizeof(kif->kf_path));
diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c
index aa48bd596d5..f8f639c04e4 100644
--- a/sys/kern/kern_proc.c
+++ b/sys/kern/kern_proc.c
@@ -1440,11 +1440,11 @@ sysctl_kern_proc_vmmap(SYSCTL_HANDLER_ARGS)
 			kve->kve_shadow_count = obj->shadow_count;
 			VM_OBJECT_UNLOCK(obj);
 			if (vp != NULL) {
-				vfslocked = VFS_LOCK_GIANT(vp->v_mount);
-				vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 				vn_fullpath(curthread, vp, &fullpath,
 				    &freepath);
 				cred = curthread->td_ucred;
+				vfslocked = VFS_LOCK_GIANT(vp->v_mount);
+				vn_lock(vp, LK_SHARED | LK_RETRY);
 				if (VOP_GETATTR(vp, &va, cred) == 0) {
 					kve->kve_fileid = va.va_fileid;
 					kve->kve_fsid = va.va_fsid;