git: 247f652e622d - stable/13 - cache: make ->nc_flag accesses atomic-clean for lockless usage

[Mateusz Guzik]

The branch stable/13 has been updated by mjg:

URL: https://cgit.FreeBSD.org/src/commit/?id=247f652e622d9aebda627ea34ba5af242dbb835e

commit 247f652e622d9aebda627ea34ba5af242dbb835e
Author:     Mateusz Guzik <mjg at FreeBSD.org>
AuthorDate: 2021-01-25 20:58:59 +0000
Commit:     Mateusz Guzik <mjg at FreeBSD.org>
CommitDate: 2021-02-01 12:39:17 +0000

    cache: make ->nc_flag accesses atomic-clean for lockless usage
    
    (cherry picked from commit 6ef8fede86f3feed7fb1e15b0e8a32ecfec33c6c)
---
 sys/kern/vfs_cache.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 9d5b18aa4132..ba3856ffe0b4 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -398,7 +398,7 @@ static inline struct negstate *
 NCP2NEGSTATE(struct namecache *ncp)
 {
 
-	MPASS(ncp->nc_flag & NCF_NEGATIVE);
+	MPASS(atomic_load_char(&ncp->nc_flag) & NCF_NEGATIVE);
 	return (&ncp->nc_neg);
 }
 
@@ -1994,7 +1994,7 @@ negative_success:
 	}
 
 	cache_out_ts(ncp, tsp, ticksp);
-	whiteout = (ncp->nc_flag & NCF_WHITE);
+	whiteout = (atomic_load_char(&ncp->nc_flag) & NCF_WHITE);
 	neg_promote = cache_neg_hit_prep(ncp);
 	if (!cache_ncp_canuse(ncp)) {
 		cache_neg_hit_abort(ncp);
@@ -2149,6 +2149,7 @@ cache_enter_lock(struct celockstate *cel, struct vnode *dvp, struct vnode *vp,
 {
 	struct namecache *ncp;
 	struct mtx *blps[2];
+	u_char nc_flag;
 
 	blps[0] = HASH2BUCKETLOCK(hash);
 	for (;;) {
@@ -2159,11 +2160,12 @@ cache_enter_lock(struct celockstate *cel, struct vnode *dvp, struct vnode *vp,
 		ncp = vp->v_cache_dd;
 		if (ncp == NULL)
 			break;
-		if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
+		nc_flag = atomic_load_char(&ncp->nc_flag);
+		if ((nc_flag & NCF_ISDOTDOT) == 0)
 			break;
 		MPASS(ncp->nc_dvp == vp);
 		blps[1] = NCP2BUCKETLOCK(ncp);
-		if (ncp->nc_flag & NCF_NEGATIVE)
+		if ((nc_flag & NCF_NEGATIVE) != 0)
 			break;
 		if (cache_lock_vnodes_cel_3(cel, ncp->nc_vp))
 			break;
@@ -2190,6 +2192,7 @@ cache_enter_lock_dd(struct celockstate *cel, struct vnode *dvp, struct vnode *vp
 {
 	struct namecache *ncp;
 	struct mtx *blps[2];
+	u_char nc_flag;
 
 	blps[0] = HASH2BUCKETLOCK(hash);
 	for (;;) {
@@ -2198,11 +2201,12 @@ cache_enter_lock_dd(struct celockstate *cel, struct vnode *dvp, struct vnode *vp
 		ncp = dvp->v_cache_dd;
 		if (ncp == NULL)
 			break;
-		if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
+		nc_flag = atomic_load_char(&ncp->nc_flag);
+		if ((nc_flag & NCF_ISDOTDOT) == 0)
 			break;
 		MPASS(ncp->nc_dvp == dvp);
 		blps[1] = NCP2BUCKETLOCK(ncp);
-		if (ncp->nc_flag & NCF_NEGATIVE)
+		if ((nc_flag & NCF_NEGATIVE) != 0)
 			break;
 		if (cache_lock_vnodes_cel_3(cel, ncp->nc_vp))
 			break;
@@ -2436,7 +2440,7 @@ cache_enter_time(struct vnode *dvp, struct vnode *vp, struct componentname *cnp,
 		    vp);
 	} else {
 		if (cnp->cn_flags & ISWHITEOUT)
-			ncp->nc_flag |= NCF_WHITE;
+			atomic_store_char(&ncp->nc_flag, ncp->nc_flag | NCF_WHITE);
 		cache_neg_insert(ncp);
 		SDT_PROBE2(vfs, namecache, enter_negative, done, dvp,
 		    ncp->nc_name);