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cache: change ->v_cache_dd synchronisation rules

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Instead of resorting to seqc modification take advantage of immutability
of entries and check if the entry still matches after everything got
prepared.
This commit is contained in:
Mateusz Guzik 2021-01-25 21:49:09 +01:00
parent 6f08427649
commit e7cf562a40
1 changed files with 24 additions and 22 deletions
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46
sys/kern/vfs_cache.c
View file

@ -1440,9 +1440,7 @@ cache_zap_locked(struct namecache *ncp)
SDT_PROBE3(vfs, namecache, zap, done, dvp, ncp->nc_name, vp);
TAILQ_REMOVE(&vp->v_cache_dst, ncp, nc_dst);
if (ncp == vp->v_cache_dd) {
vn_seqc_write_begin_unheld(vp);
atomic_store_ptr(&vp->v_cache_dd, NULL);
vn_seqc_write_end(vp);
}
} else {
SDT_PROBE2(vfs, namecache, zap_negative, done, dvp, ncp->nc_name);
@ -1450,9 +1448,7 @@ cache_zap_locked(struct namecache *ncp)
}
if (ncp->nc_flag & NCF_ISDOTDOT) {
if (ncp == dvp->v_cache_dd) {
vn_seqc_write_begin_unheld(dvp);
atomic_store_ptr(&dvp->v_cache_dd, NULL);
vn_seqc_write_end(dvp);
}
} else {
LIST_REMOVE(ncp, nc_src);
@ -1627,9 +1623,7 @@ retry_dotdot:
mtx_unlock(dvlp2);
cache_free(ncp);
} else {
vn_seqc_write_begin(dvp);
atomic_store_ptr(&dvp->v_cache_dd, NULL);
vn_seqc_write_end(dvp);
mtx_unlock(dvlp);
if (dvlp2 != NULL)
mtx_unlock(dvlp2);
@ -2246,7 +2240,6 @@ cache_enter_dotdot_prep(struct vnode *dvp, struct vnode *vp,
cache_celockstate_init(&cel);
hash = cache_get_hash(cnp->cn_nameptr, len, dvp);
cache_enter_lock_dd(&cel, dvp, vp, hash);
vn_seqc_write_begin(dvp);
ncp = dvp->v_cache_dd;
if (ncp != NULL && (ncp->nc_flag & NCF_ISDOTDOT)) {
KASSERT(ncp->nc_dvp == dvp, ("wrong isdotdot parent"));
@ -2255,7 +2248,6 @@ cache_enter_dotdot_prep(struct vnode *dvp, struct vnode *vp,
ncp = NULL;
}
atomic_store_ptr(&dvp->v_cache_dd, NULL);
vn_seqc_write_end(dvp);
cache_enter_unlock(&cel);
if (ncp != NULL)
cache_free(ncp);
@ -2392,9 +2384,8 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp, struct componentname *cnp,
goto out_unlock_free;
KASSERT(vp == NULL || vp->v_type == VDIR,
("wrong vnode type %p", vp));
vn_seqc_write_begin(dvp);
atomic_thread_fence_rel();
atomic_store_ptr(&dvp->v_cache_dd, ncp);
vn_seqc_write_end(dvp);
}
if (vp != NULL) {
@ -2404,20 +2395,17 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp, struct componentname *cnp,
* directory name in it and the name ".." for the
* directory's parent.
*/
vn_seqc_write_begin(vp);
if ((ndd = vp->v_cache_dd) != NULL) {
if ((ndd->nc_flag & NCF_ISDOTDOT) != 0)
cache_zap_locked(ndd);
else
ndd = NULL;
}
atomic_thread_fence_rel();
atomic_store_ptr(&vp->v_cache_dd, ncp);
vn_seqc_write_end(vp);
} else if (vp->v_type != VDIR) {
if (vp->v_cache_dd != NULL) {
vn_seqc_write_begin(vp);
atomic_store_ptr(&vp->v_cache_dd, NULL);
vn_seqc_write_end(vp);
}
}
}
@ -3301,10 +3289,6 @@ vn_fullpath_any_smr(struct vnode *vp, struct vnode *rdir, char *buf,
cache_rev_failed(&reason);
goto out_abort;
}
if (!cache_ncp_canuse(ncp)) {
cache_rev_failed(&reason);
goto out_abort;
}
if (ncp->nc_nlen >= *buflen) {
cache_rev_failed(&reason);
error = ENOMEM;
@ -3324,6 +3308,17 @@ vn_fullpath_any_smr(struct vnode *vp, struct vnode *rdir, char *buf,
cache_rev_failed(&reason);
goto out_abort;
}
/*
* Acquire fence provided by vn_seqc_read_any above.
*/
if (__predict_false(atomic_load_ptr(&vp->v_cache_dd) != ncp)) {
cache_rev_failed(&reason);
goto out_abort;
}
if (!cache_ncp_canuse(ncp)) {
cache_rev_failed(&reason);
goto out_abort;
}
vp = tvp;
vp_seqc = tvp_seqc;
if (vp == rdir || vp == rootvnode)
@ -4719,15 +4714,22 @@ cache_fplookup_dotdot(struct cache_fpl *fpl)
fpl->tvp = ncp->nc_dvp;
}
if (!cache_ncp_canuse(ncp)) {
return (cache_fpl_aborted(fpl));
}
fpl->tvp_seqc = vn_seqc_read_any(fpl->tvp);
if (seqc_in_modify(fpl->tvp_seqc)) {
return (cache_fpl_partial(fpl));
}
/*
* Acquire fence provided by vn_seqc_read_any above.
*/
if (__predict_false(atomic_load_ptr(&dvp->v_cache_dd) != ncp)) {
return (cache_fpl_aborted(fpl));
}
if (!cache_ncp_canuse(ncp)) {
return (cache_fpl_aborted(fpl));
}
counter_u64_add(dotdothits, 1);
return (0);
}