[v2,3/5] cifs: don't take exclusive lock for updating target hints

Commit Message

Paulo Alcantara Jan. 17, 2023, 10 p.m. UTC

Avoid contention while updating dfs target hints.  This should be
perfectly fine to update them under shared locks.

Signed-off-by: Paulo Alcantara (SUSE) <[e-mail]>
---
 fs/cifs/dfs_cache.c | 47 +++++++++++++++++++--------------------------
 1 file changed, 20 insertions(+), 27 deletions(-)

Patch

diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c
index 755a00c4cba1..19847f9114ba 100644
--- a/fs/cifs/dfs_cache.c
+++ b/fs/cifs/dfs_cache.c
@@ -269,7 +269,7 @@  static int dfscache_proc_show(struct seq_file *m, void *v)
 			list_for_each_entry(t, &ce->tlist, list) {
 				seq_printf(m, "  %s%s\n",
 					   t->name,
-					   ce->tgthint == t ? " (target hint)" : "");
+					   READ_ONCE(ce->tgthint) == t ? " (target hint)" : "");
 			}
 		}
 	}
@@ -321,7 +321,7 @@  static inline void dump_tgts(const struct cache_entry *ce)
 	cifs_dbg(FYI, "target list:\n");
 	list_for_each_entry(t, &ce->tlist, list) {
 		cifs_dbg(FYI, "  %s%s\n", t->name,
-			 ce->tgthint == t ? " (target hint)" : "");
+			 READ_ONCE(ce->tgthint) == t ? " (target hint)" : "");
 	}
 }
 
@@ -427,7 +427,7 @@  static int cache_entry_hash(const void *data, int size, unsigned int *hash)
 /* Return target hint of a DFS cache entry */
 static inline char *get_tgt_name(const struct cache_entry *ce)
 {
-	struct cache_dfs_tgt *t = ce->tgthint;
+	struct cache_dfs_tgt *t = READ_ONCE(ce->tgthint);
 
 	return t ? t->name : ERR_PTR(-ENOENT);
 }
@@ -470,6 +470,7 @@  static struct cache_dfs_tgt *alloc_target(const char *name, int path_consumed)
 static int copy_ref_data(const struct dfs_info3_param *refs, int numrefs,
 			 struct cache_entry *ce, const char *tgthint)
 {
+	struct cache_dfs_tgt *target;
 	int i;
 
 	ce->ttl = max_t(int, refs[0].ttl, CACHE_MIN_TTL);
@@ -496,8 +497,9 @@  static int copy_ref_data(const struct dfs_info3_param *refs, int numrefs,
 		ce->numtgts++;
 	}
 
-	ce->tgthint = list_first_entry_or_null(&ce->tlist,
-					       struct cache_dfs_tgt, list);
+	target = list_first_entry_or_null(&ce->tlist, struct cache_dfs_tgt,
+					  list);
+	WRITE_ONCE(ce->tgthint, target);
 
 	return 0;
 }
@@ -712,14 +714,15 @@  void dfs_cache_destroy(void)
 static int update_cache_entry_locked(struct cache_entry *ce, const struct dfs_info3_param *refs,
 				     int numrefs)
 {
+	struct cache_dfs_tgt *target;
+	char *th = NULL;
 	int rc;
-	char *s, *th = NULL;
 
 	WARN_ON(!rwsem_is_locked(&htable_rw_lock));
 
-	if (ce->tgthint) {
-		s = ce->tgthint->name;
-		th = kstrdup(s, GFP_ATOMIC);
+	target = READ_ONCE(ce->tgthint);
+	if (target) {
+		th = kstrdup(target->name, GFP_ATOMIC);
 		if (!th)
 			return -ENOMEM;
 	}
@@ -896,7 +899,7 @@  static int get_targets(struct cache_entry *ce, struct dfs_cache_tgt_list *tl)
 		}
 		it->it_path_consumed = t->path_consumed;
 
-		if (ce->tgthint == t)
+		if (READ_ONCE(ce->tgthint) == t)
 			list_add(&it->it_list, head);
 		else
 			list_add_tail(&it->it_list, head);
@@ -1052,23 +1055,14 @@  int dfs_cache_update_tgthint(const unsigned int xid, struct cifs_ses *ses,
 		goto out_free_path;
 	}
 
-	up_read(&htable_rw_lock);
-	down_write(&htable_rw_lock);
-
-	ce = lookup_cache_entry(npath);
-	if (IS_ERR(ce)) {
-		rc = PTR_ERR(ce);
-		goto out_unlock;
-	}
-
-	t = ce->tgthint;
+	t = READ_ONCE(ce->tgthint);
 
 	if (likely(!strcasecmp(it->it_name, t->name)))
 		goto out_unlock;
 
 	list_for_each_entry(t, &ce->tlist, list) {
 		if (!strcasecmp(t->name, it->it_name)) {
-			ce->tgthint = t;
+			WRITE_ONCE(ce->tgthint, t);
 			cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
 				 it->it_name);
 			break;
@@ -1076,7 +1070,7 @@  int dfs_cache_update_tgthint(const unsigned int xid, struct cifs_ses *ses,
 	}
 
 out_unlock:
-	up_write(&htable_rw_lock);
+	up_read(&htable_rw_lock);
 out_free_path:
 	kfree(npath);
 	return rc;
@@ -1106,21 +1100,20 @@  void dfs_cache_noreq_update_tgthint(const char *path, const struct dfs_cache_tgt
 
 	cifs_dbg(FYI, "%s: path: %s\n", __func__, path);
 
-	if (!down_write_trylock(&htable_rw_lock))
-		return;
+	down_read(&htable_rw_lock);
 
 	ce = lookup_cache_entry(path);
 	if (IS_ERR(ce))
 		goto out_unlock;
 
-	t = ce->tgthint;
+	t = READ_ONCE(ce->tgthint);
 
 	if (unlikely(!strcasecmp(it->it_name, t->name)))
 		goto out_unlock;
 
 	list_for_each_entry(t, &ce->tlist, list) {
 		if (!strcasecmp(t->name, it->it_name)) {
-			ce->tgthint = t;
+			WRITE_ONCE(ce->tgthint, t);
 			cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
 				 it->it_name);
 			break;
@@ -1128,7 +1121,7 @@  void dfs_cache_noreq_update_tgthint(const char *path, const struct dfs_cache_tgt
 	}
 
 out_unlock:
-	up_write(&htable_rw_lock);
+	up_read(&htable_rw_lock);
 }
 
 /**