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cache: add NCF_WIP flag

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This allows making half-constructed entries visible to the lockless lookup,
which now can check for either "not yet fully constructed" and "no longer valid"
state.

This will be used for .. lookup.
This commit is contained in:
Mateusz Guzik 2020-08-04 23:07:00 +00:00
parent 6e10434c02
commit b403aa126e
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=363873
1 changed files with 18 additions and 11 deletions
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29
sys/kern/vfs_cache.c
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@ -162,6 +162,7 @@ struct namecache_ts {
#define NCF_DVDROP 0x10
#define NCF_NEGATIVE 0x20
#define NCF_INVALID 0x40
#define NCF_WIP 0x80
/*
* Flags in negstate.neg_flag
@ -179,22 +180,22 @@ cache_ncp_invalidate(struct namecache *ncp)
KASSERT((ncp->nc_flag & NCF_INVALID) == 0,
("%s: entry %p already invalid", __func__, ncp));
ncp->nc_flag |= NCF_INVALID;
atomic_store_char(&ncp->nc_flag, ncp->nc_flag | NCF_INVALID);
atomic_thread_fence_rel();
}
/*
* Verify validity of an entry.
* Check whether the entry can be safely used.
*
* All places which elide locks are supposed to call this after they are
* done with reading from an entry.
*/
static bool
cache_ncp_invalid(struct namecache *ncp)
cache_ncp_canuse(struct namecache *ncp)
{
atomic_thread_fence_acq();
return ((ncp->nc_flag & NCF_INVALID) != 0);
return ((atomic_load_char(&ncp->nc_flag) & (NCF_INVALID | NCF_WIP)) == 0);
}
/*
@ -1506,7 +1507,7 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp,
VOP_UNLOCK(dvp);
}
if (doing_smr) {
if (cache_ncp_invalid(ncp)) {
if (!cache_ncp_canuse(ncp)) {
vfs_smr_exit();
*vpp = NULL;
goto retry;
@ -1560,7 +1561,7 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp,
*/
negstate = NCP2NEGSTATE(ncp);
if ((negstate->neg_flag & NEG_HOT) == 0 ||
cache_ncp_invalid(ncp)) {
!cache_ncp_canuse(ncp)) {
vfs_smr_exit();
doing_smr = false;
goto retry_hashed;
@ -1884,7 +1885,7 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp, struct componentname *cnp,
* namecache entry as possible before acquiring the lock.
*/
ncp = cache_alloc(cnp->cn_namelen, tsp != NULL);
ncp->nc_flag = flag;
ncp->nc_flag = flag | NCF_WIP;
ncp->nc_vp = vp;
if (vp == NULL)
cache_negative_init(ncp);
@ -1987,13 +1988,19 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp, struct componentname *cnp,
ncp->nc_name);
}
atomic_thread_fence_rel();
/*
* Insert the new namecache entry into the appropriate chain
* within the cache entries table.
*/
CK_LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
atomic_thread_fence_rel();
/*
* Mark the entry as fully constructed.
* It is immutable past this point until its removal.
*/
atomic_store_char(&ncp->nc_flag, ncp->nc_flag & ~NCF_WIP);
cache_enter_unlock(&cel);
if (numneg * ncnegfactor > lnumcache)
cache_negative_zap_one();
@ -3197,7 +3204,7 @@ cache_fplookup_negative_promote(struct cache_fpl *fpl, struct namecache *oncp,
goto out_abort;
}
if (__predict_false(cache_ncp_invalid(ncp))) {
if (__predict_false(!cache_ncp_canuse(ncp))) {
goto out_abort;
}
@ -3458,7 +3465,7 @@ cache_fplookup_next(struct cache_fpl *fpl)
if ((nc_flag & NCF_NEGATIVE) != 0) {
negstate = NCP2NEGSTATE(ncp);
neg_hot = ((negstate->neg_flag & NEG_HOT) != 0);
if (__predict_false(cache_ncp_invalid(ncp))) {
if (__predict_false(!cache_ncp_canuse(ncp))) {
return (cache_fpl_partial(fpl));
}
if (__predict_false((nc_flag & NCF_WHITE) != 0)) {
@ -3474,7 +3481,7 @@ cache_fplookup_next(struct cache_fpl *fpl)
return (cache_fpl_handled(fpl, ENOENT));
}
if (__predict_false(cache_ncp_invalid(ncp))) {
if (__predict_false(!cache_ncp_canuse(ncp))) {
return (cache_fpl_partial(fpl));
}