namecache: factor out ~MAKEENTRY lookups from the common path
Lookups of the sort are rare compared to regular ones and succesfull ones result in removing entries from the cache. In the current code buckets are rlocked and a trylock dance is performed, which can fail and cause a restart. Fixing it will require a little bit of surgery and in order to keep the code maintaineable the 2 cases have to split. MFC after: 1 week
This commit is contained in:
Mateusz Guzik
parent
f38c0c46c5
commit
709939a7b7
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=324378
@ -1058,7 +1058,6 @@ cache_lookup_unlock(struct rwlock *blp, struct mtx *vlp)
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if (blp != NULL) {
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rw_runlock(blp);
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mtx_assert(vlp, MA_NOTOWNED);
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} else {
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mtx_unlock(vlp);
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}
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@ -1117,6 +1116,82 @@ cache_lookup_dot(struct vnode *dvp, struct vnode **vpp, struct componentname *cn
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* not recursively acquired.
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*/
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static __noinline int
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cache_lookup_nomakeentry(struct vnode *dvp, struct vnode **vpp,
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struct componentname *cnp, struct timespec *tsp, int *ticksp)
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{
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struct namecache *ncp;
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struct rwlock *blp;
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struct mtx *dvlp, *dvlp2;
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uint32_t hash;
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int error;
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if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
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counter_u64_add(dotdothits, 1);
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dvlp = VP2VNODELOCK(dvp);
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dvlp2 = NULL;
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mtx_lock(dvlp);
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retry_dotdot:
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ncp = dvp->v_cache_dd;
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if (ncp == NULL) {
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SDT_PROBE3(vfs, namecache, lookup, miss, dvp,
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"..", NULL);
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mtx_unlock(dvlp);
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return (0);
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}
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if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) {
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if (ncp->nc_dvp != dvp)
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panic("dvp %p v_cache_dd %p\n", dvp, ncp);
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if (!cache_zap_locked_vnode_kl2(ncp,
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dvp, &dvlp2))
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goto retry_dotdot;
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MPASS(dvp->v_cache_dd == NULL);
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mtx_unlock(dvlp);
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if (dvlp2 != NULL)
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mtx_unlock(dvlp2);
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cache_free(ncp);
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} else {
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dvp->v_cache_dd = NULL;
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mtx_unlock(dvlp);
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if (dvlp2 != NULL)
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mtx_unlock(dvlp2);
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}
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return (0);
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}
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hash = cache_get_hash(cnp->cn_nameptr, cnp->cn_namelen, dvp);
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blp = HASH2BUCKETLOCK(hash);
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retry:
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rw_rlock(blp);
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LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
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counter_u64_add(numchecks, 1);
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if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen &&
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!bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen))
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break;
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}
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/* We failed to find an entry */
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if (ncp == NULL) {
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rw_runlock(blp);
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SDT_PROBE3(vfs, namecache, lookup, miss, dvp, cnp->cn_nameptr,
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NULL);
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counter_u64_add(nummisszap, 1);
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return (0);
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}
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counter_u64_add(numposzaps, 1);
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error = cache_zap_rlocked_bucket(ncp, blp);
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if (error != 0) {
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zap_and_exit_bucket_fail++;
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cache_maybe_yield();
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goto retry;
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}
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cache_free(ncp);
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return (0);
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}
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int
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cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp,
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struct timespec *tsp, int *ticksp)
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@ -1132,69 +1207,51 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp,
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cnp->cn_flags &= ~MAKEENTRY;
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return (0);
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}
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retry:
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blp = NULL;
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dvlp = VP2VNODELOCK(dvp);
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error = 0;
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counter_u64_add(numcalls, 1);
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if (cnp->cn_nameptr[0] == '.') {
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if (cnp->cn_namelen == 1)
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return (cache_lookup_dot(dvp, vpp, cnp, tsp, ticksp));
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if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
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counter_u64_add(dotdothits, 1);
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dvlp2 = NULL;
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mtx_lock(dvlp);
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retry_dotdot:
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ncp = dvp->v_cache_dd;
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if (ncp == NULL) {
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SDT_PROBE3(vfs, namecache, lookup, miss, dvp,
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"..", NULL);
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mtx_unlock(dvlp);
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return (0);
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}
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if ((cnp->cn_flags & MAKEENTRY) == 0) {
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if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) {
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if (ncp->nc_dvp != dvp)
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panic("dvp %p v_cache_dd %p\n", dvp, ncp);
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if (!cache_zap_locked_vnode_kl2(ncp,
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dvp, &dvlp2))
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goto retry_dotdot;
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MPASS(dvp->v_cache_dd == NULL);
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mtx_unlock(dvlp);
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if (dvlp2 != NULL)
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mtx_unlock(dvlp2);
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cache_free(ncp);
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} else {
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dvp->v_cache_dd = NULL;
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mtx_unlock(dvlp);
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if (dvlp2 != NULL)
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mtx_unlock(dvlp2);
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}
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return (0);
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}
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if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) {
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if (ncp->nc_flag & NCF_NEGATIVE)
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*vpp = NULL;
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else
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*vpp = ncp->nc_vp;
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} else
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*vpp = ncp->nc_dvp;
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/* Return failure if negative entry was found. */
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if (*vpp == NULL)
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goto negative_success;
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CTR3(KTR_VFS, "cache_lookup(%p, %s) found %p via ..",
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dvp, cnp->cn_nameptr, *vpp);
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SDT_PROBE3(vfs, namecache, lookup, hit, dvp, "..",
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*vpp);
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cache_out_ts(ncp, tsp, ticksp);
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if ((ncp->nc_flag & (NCF_ISDOTDOT | NCF_DTS)) ==
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NCF_DTS && tsp != NULL) {
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ncp_ts = __containerof(ncp, struct namecache_ts, nc_nc);
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*tsp = ncp_ts->nc_dotdottime;
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}
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goto success;
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if (__predict_false(cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.'))
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return (cache_lookup_dot(dvp, vpp, cnp, tsp, ticksp));
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if ((cnp->cn_flags & MAKEENTRY) == 0)
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return (cache_lookup_nomakeentry(dvp, vpp, cnp, tsp, ticksp));
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retry:
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blp = NULL;
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error = 0;
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if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
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counter_u64_add(dotdothits, 1);
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dvlp = VP2VNODELOCK(dvp);
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dvlp2 = NULL;
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mtx_lock(dvlp);
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ncp = dvp->v_cache_dd;
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if (ncp == NULL) {
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SDT_PROBE3(vfs, namecache, lookup, miss, dvp,
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"..", NULL);
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mtx_unlock(dvlp);
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return (0);
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}
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if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) {
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if (ncp->nc_flag & NCF_NEGATIVE)
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*vpp = NULL;
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else
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*vpp = ncp->nc_vp;
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} else
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*vpp = ncp->nc_dvp;
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/* Return failure if negative entry was found. */
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if (*vpp == NULL)
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goto negative_success;
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CTR3(KTR_VFS, "cache_lookup(%p, %s) found %p via ..",
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dvp, cnp->cn_nameptr, *vpp);
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SDT_PROBE3(vfs, namecache, lookup, hit, dvp, "..",
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*vpp);
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cache_out_ts(ncp, tsp, ticksp);
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if ((ncp->nc_flag & (NCF_ISDOTDOT | NCF_DTS)) ==
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NCF_DTS && tsp != NULL) {
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ncp_ts = __containerof(ncp, struct namecache_ts, nc_nc);
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*tsp = ncp_ts->nc_dotdottime;
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}
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goto success;
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}
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hash = cache_get_hash(cnp->cn_nameptr, cnp->cn_namelen, dvp);
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@ -1210,23 +1267,13 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp,
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/* We failed to find an entry */
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if (ncp == NULL) {
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rw_runlock(blp);
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SDT_PROBE3(vfs, namecache, lookup, miss, dvp, cnp->cn_nameptr,
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NULL);
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if ((cnp->cn_flags & MAKEENTRY) == 0) {
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counter_u64_add(nummisszap, 1);
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} else {
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counter_u64_add(nummiss, 1);
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}
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cache_lookup_unlock(blp, dvlp);
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counter_u64_add(nummiss, 1);
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return (0);
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}
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/* We don't want to have an entry, so dump it */
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if ((cnp->cn_flags & MAKEENTRY) == 0) {
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counter_u64_add(numposzaps, 1);
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goto zap_and_exit;
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}
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/* We found a "positive" match, return the vnode */
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if (!(ncp->nc_flag & NCF_NEGATIVE)) {
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counter_u64_add(numposhits, 1);
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