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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.

(cherry picked from commit e7cf562a40)
This commit is contained in:
Mateusz Guzik 2021-01-25 21:49:09 +01:00
parent 9375a93b6c
commit 1f28a3afe4
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);
}