Date: Thu, 9 Oct 2008 20:40:11 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-7@freebsd.org Subject: svn commit: r183732 - in stable/7/sys: . kern Message-ID: <200810092040.m99KeBIN071046@svn.freebsd.org>
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Author: jhb Date: Thu Oct 9 20:40:11 2008 New Revision: 183732 URL: http://svn.freebsd.org/changeset/base/183732 Log: MFC: Check for duplicate attempts to add the same positive entry to the name cache. If a duplicate attempt is made, just do nothing. This fixes a race with shared locking in pathname lockups. Approved by: re (kib) Modified: stable/7/sys/ (props changed) stable/7/sys/kern/vfs_cache.c Modified: stable/7/sys/kern/vfs_cache.c ============================================================================== --- stable/7/sys/kern/vfs_cache.c Thu Oct 9 20:09:56 2008 (r183731) +++ stable/7/sys/kern/vfs_cache.c Thu Oct 9 20:40:11 2008 (r183732) @@ -496,8 +496,39 @@ cache_enter(dvp, vp, cnp) hold = 0; zap = 0; + + /* + * Calculate the hash key and setup as much of the new + * namecache entry as possible before acquiring the lock. + */ ncp = cache_alloc(cnp->cn_namelen); + ncp->nc_vp = vp; + ncp->nc_dvp = dvp; + len = ncp->nc_nlen = cnp->cn_namelen; + hash = fnv_32_buf(cnp->cn_nameptr, len, FNV1_32_INIT); + bcopy(cnp->cn_nameptr, ncp->nc_name, len); + hash = fnv_32_buf(&dvp, sizeof(dvp), hash); CACHE_LOCK(); + + /* + * See if this vnode is already in the cache with this name. + * This can happen with concurrent lookups of the same path + * name. + */ + if (vp) { + struct namecache *n2; + + TAILQ_FOREACH(n2, &vp->v_cache_dst, nc_dst) { + if (n2->nc_dvp == dvp && + n2->nc_nlen == cnp->cn_namelen && + !bcmp(n2->nc_name, cnp->cn_nameptr, n2->nc_nlen)) { + CACHE_UNLOCK(); + cache_free(ncp); + return; + } + } + } + numcache++; if (!vp) { numneg++; @@ -509,16 +540,9 @@ cache_enter(dvp, vp, cnp) } /* - * Set the rest of the namecache entry elements, calculate it's - * hash key and insert it into the appropriate chain within - * the cache entries table. + * Insert the new namecache entry into the appropriate chain + * within the cache entries table. */ - ncp->nc_vp = vp; - ncp->nc_dvp = dvp; - len = ncp->nc_nlen = cnp->cn_namelen; - hash = fnv_32_buf(cnp->cn_nameptr, len, FNV1_32_INIT); - bcopy(cnp->cn_nameptr, ncp->nc_name, len); - hash = fnv_32_buf(&dvp, sizeof(dvp), hash); ncpp = NCHHASH(hash); LIST_INSERT_HEAD(ncpp, ncp, nc_hash); if (LIST_EMPTY(&dvp->v_cache_src)) {
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