From 950a571078f24c9d58281a7ebaac55c569cdb408 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Fri, 11 Apr 2014 19:02:21 +0000
Subject: [PATCH 08/14] Omit needless lock dances in msdosfs_lookup.
---
sys/fs/msdosfs/msdosfs_lookup.c | 64 +++--------------------------------------
1 file changed, 4 insertions(+), 60 deletions(-)
diff --git a/sys/fs/msdosfs/msdosfs_lookup.c b/sys/fs/msdosfs/msdosfs_lookup.c
index 01e8dd0..f23b52c 100644
--- a/sys/fs/msdosfs/msdosfs_lookup.c
+++ b/sys/fs/msdosfs/msdosfs_lookup.c
@@ -113,7 +113,6 @@ msdosfs_lookup(void *v)
int blsize;
int isadir; /* ~0 if found direntry is a directory */
u_long scn; /* starting cluster number */
- struct vnode *pdp;
struct denode *dp;
struct denode *tdp;
struct msdosfsmount *pmp;
@@ -493,13 +492,7 @@ foundroot:
}
if ((error = deget(pmp, cluster, blkoff, 0, &tdp)) != 0)
return (error);
- /* XXX Omit needless lock/unlock. */
- if ((error = vn_lock(DETOV(tdp), LK_EXCLUSIVE)) != 0) {
- vrele(DETOV(tdp));
- return (error);
- }
*vpp = DETOV(tdp);
- VOP_UNLOCK(*vpp);
return (0);
}
@@ -530,63 +523,17 @@ foundroot:
if ((error = deget(pmp, cluster, blkoff, 0, &tdp)) != 0)
return (error);
- /* XXX Omit needless lock/unlock. */
- if ((error = vn_lock(DETOV(tdp), LK_EXCLUSIVE)) != 0) {
- vrele(DETOV(tdp));
- return (error);
- }
*vpp = DETOV(tdp);
- VOP_UNLOCK(*vpp);
return (0);
}
- /*
- * Step through the translation in the name. We do not `vput' the
- * directory because we may need it again if a symbolic link
- * is relative to the current directory. Instead we save it
- * unlocked as "pdp". We must get the target inode before unlocking
- * the directory to insure that the inode will not be removed
- * before we get it. We prevent deadlock by always fetching
- * inodes from the root, moving down the directory tree. Thus
- * when following backward pointers ".." we must unlock the
- * parent directory before getting the requested directory.
- * There is a potential race condition here if both the current
- * and parent directories are removed before the VFS_VGET for the
- * inode associated with ".." returns. We hope that this occurs
- * infrequently since we cannot avoid this race condition without
- * implementing a sophisticated deadlock detection algorithm.
- * Note also that this simple deadlock detection scheme will not
- * work if the file system has any hard links other than ".."
- * that point backwards in the directory structure.
- */
- pdp = vdp;
- if (flags & ISDOTDOT) {
- VOP_UNLOCK(pdp); /* race to get the inode */
- error = deget(pmp, cluster, blkoff, 0, &tdp);
- if (error) {
- vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY);
- return error;
- }
- /* XXX Omit needless lock/unlock. */
- error = vn_lock(DETOV(tdp), LK_EXCLUSIVE);
- if (error) {
- vrele(DETOV(tdp));
- vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY);
- return error;
- }
- vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY);
- *vpp = DETOV(tdp);
- } else if (dp->de_StartCluster == scn && isadir) {
+ if (dp->de_StartCluster == scn && isadir) {
vref(vdp); /* we want ourself, ie "." */
*vpp = vdp;
} else {
- if ((error = deget(pmp, cluster, blkoff, 0, &tdp)) != 0)
- return (error);
- /* XXX Omit needless lock/unlock. */
- if ((error = vn_lock(DETOV(tdp), LK_EXCLUSIVE)) != 0) {
- vrele(DETOV(tdp));
- return (error);
- }
+ error = deget(pmp, cluster, blkoff, 0, &tdp);
+ if (error)
+ return error;
*vpp = DETOV(tdp);
}
@@ -595,9 +542,6 @@ foundroot:
*/
cache_enter(vdp, *vpp, cnp->cn_nameptr, cnp->cn_namelen, cnp->cn_flags);
- if (*vpp != vdp)
- VOP_UNLOCK(*vpp);
-
return 0;
}
#endif /* _KERNEL */
--
1.8.3.1