From: Paulo Alcantara <pc@cjr.nz>
Date: Tue, 8 Jun 2021 13:50:06 -0300
Subject: [PATCH] cifs: avoid starvation when refreshing dfs cache
Git-commit: 1023e90b733acd1da98ba7067aa0fa8b998eed19
References: bsc#1185902
Patch-mainline: v5.14-rc1
When refreshing the DFS cache, keep SMB2 IOCTL calls as much outside
critical sections as possible and avoid read/write starvation when
getting new DFS referrals by using broken or slow connections.
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Acked-by: Paulo Alcantara <palcantara@suse.de>
---
fs/cifs/dfs_cache.c | 145 ++++++++++++++++++++++++++++++++------------
1 file changed, 105 insertions(+), 40 deletions(-)
diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c
index d9c2c75a2989..775dbc7b0d7a 100644
--- a/fs/cifs/dfs_cache.c
+++ b/fs/cifs/dfs_cache.c
@@ -554,6 +554,8 @@ static void remove_oldest_entry_locked(void)
struct cache_entry *ce;
struct cache_entry *to_del = NULL;
+ WARN_ON(!rwsem_is_locked(&htable_rw_lock));
+
for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
struct hlist_head *l = &cache_htable[i];
@@ -583,7 +585,13 @@ static int add_cache_entry_locked(struct dfs_info3_param *refs, int numrefs)
struct cache_entry *ce;
unsigned int hash;
- convert_delimiter(refs[0].path_name, '\\');
+ WARN_ON(!rwsem_is_locked(&htable_rw_lock));
+
+ if (atomic_read(&cache_count) >= CACHE_MAX_ENTRIES) {
+ cifs_dbg(FYI, "%s: reached max cache size (%d)\n", __func__, CACHE_MAX_ENTRIES);
+ remove_oldest_entry_locked();
+ }
+
rc = cache_entry_hash(refs[0].path_name, strlen(refs[0].path_name), &hash);
if (rc)
return rc;
@@ -605,6 +613,8 @@ static int add_cache_entry_locked(struct dfs_info3_param *refs, int numrefs)
hlist_add_head(&ce->hlist, &cache_htable[hash]);
dump_ce(ce);
+ atomic_inc(&cache_count);
+
return 0;
}
@@ -719,16 +729,13 @@ void dfs_cache_destroy(void)
}
/* Update a cache entry with the new referral in @refs */
-static int update_cache_entry_locked(const char *path, const struct dfs_info3_param *refs,
+static int update_cache_entry_locked(struct cache_entry *ce, const struct dfs_info3_param *refs,
int numrefs)
{
int rc;
- struct cache_entry *ce;
char *s, *th = NULL;
- ce = lookup_cache_entry(path);
- if (IS_ERR(ce))
- return PTR_ERR(ce);
+ WARN_ON(!rwsem_is_locked(&htable_rw_lock));
if (ce->tgthint) {
s = ce->tgthint->name;
@@ -750,18 +757,28 @@ static int update_cache_entry_locked(const char *path, const struct dfs_info3_pa
static int get_dfs_referral(const unsigned int xid, struct cifs_ses *ses, const char *path,
struct dfs_info3_param **refs, int *numrefs)
{
+ int rc;
+ int i;
+
cifs_dbg(FYI, "%s: get an DFS referral for %s\n", __func__, path);
+ *refs = NULL;
+ *numrefs = 0;
+
if (!ses || !ses->server || !ses->server->ops->get_dfs_refer)
return -EOPNOTSUPP;
if (unlikely(!cache_cp))
return -EINVAL;
- *refs = NULL;
- *numrefs = 0;
+ rc = ses->server->ops->get_dfs_refer(xid, ses, path, refs, numrefs, cache_cp,
+ NO_MAP_UNI_RSVD);
+ if (!rc) {
+ struct dfs_info3_param *ref = *refs;
- return ses->server->ops->get_dfs_refer(xid, ses, path, refs, numrefs, cache_cp,
- NO_MAP_UNI_RSVD);
+ for (i = 0; i < *numrefs; i++)
+ convert_delimiter(ref[i].path_name, '\\');
+ }
+ return rc;
}
/*
@@ -807,18 +824,11 @@ static int cache_refresh_path(const unsigned int xid, struct cifs_ses *ses, cons
dump_refs(refs, numrefs);
if (!newent) {
- rc = update_cache_entry_locked(path, refs, numrefs);
+ rc = update_cache_entry_locked(ce, refs, numrefs);
goto out_unlock;
}
- if (atomic_read(&cache_count) >= CACHE_MAX_ENTRIES) {
- cifs_dbg(FYI, "%s: reached max cache size (%d)\n", __func__, CACHE_MAX_ENTRIES);
- remove_oldest_entry_locked();
- }
-
rc = add_cache_entry_locked(refs, numrefs);
- if (!rc)
- atomic_inc(&cache_count);
out_unlock:
up_write(&htable_rw_lock);
@@ -1313,15 +1323,43 @@ static void refresh_mounts(struct cifs_ses **sessions)
list_for_each_entry_safe(tcon, ntcon, &tcons, ulist) {
const char *path = tcon->dfs_path + 1;
+ struct cache_entry *ce;
+ struct dfs_info3_param *refs = NULL;
+ int numrefs = 0;
+ bool needs_refresh = false;
int rc = 0;
list_del_init(&tcon->ulist);
+
ses = find_ipc_from_server_path(sessions, path);
- if (!IS_ERR(ses)) {
- xid = get_xid();
- cache_refresh_path(xid, ses, path);
- free_xid(xid);
+ if (IS_ERR(ses))
+ goto next_tcon;
+
+ down_read(&htable_rw_lock);
+ ce = lookup_cache_entry(path);
+ needs_refresh = IS_ERR(ce) || cache_entry_expired(ce);
+ up_read(&htable_rw_lock);
+
+ if (!needs_refresh)
+ goto next_tcon;
+
+ xid = get_xid();
+ rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
+ free_xid(xid);
+
+ /* Create or update a cache entry with the new referral */
+ if (!rc) {
+ down_write(&htable_rw_lock);
+ ce = lookup_cache_entry(path);
+ if (IS_ERR(ce))
+ add_cache_entry_locked(refs, numrefs);
+ else if (cache_entry_expired(ce))
+ update_cache_entry_locked(ce, refs, numrefs);
+ up_write(&htable_rw_lock);
}
+
+next_tcon:
+ free_dfs_info_array(refs, numrefs);
cifs_put_tcon(tcon);
}
}
@@ -1331,40 +1369,67 @@ static void refresh_cache(struct cifs_ses **sessions)
int i;
struct cifs_ses *ses;
unsigned int xid;
- int rc;
+ char *ref_paths[CACHE_MAX_ENTRIES];
+ int count = 0;
+ struct cache_entry *ce;
/*
- * Refresh all cached entries.
+ * Refresh all cached entries. Get all new referrals outside critical section to avoid
+ * starvation while performing SMB2 IOCTL on broken or slow connections.
+
* The cache entries may cover more paths than the active mounts
* (e.g. domain-based DFS referrals or multi tier DFS setups).
*/
- down_write(&htable_rw_lock);
+ down_read(&htable_rw_lock);
for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
- struct cache_entry *ce;
struct hlist_head *l = &cache_htable[i];
hlist_for_each_entry(ce, l, hlist) {
- struct dfs_info3_param *refs = NULL;
- int numrefs = 0;
-
- if (hlist_unhashed(&ce->hlist) || !cache_entry_expired(ce))
+ if (count == ARRAY_SIZE(ref_paths))
+ goto out_unlock;
+ if (hlist_unhashed(&ce->hlist) || !cache_entry_expired(ce) ||
+ IS_ERR(find_ipc_from_server_path(sessions, ce->path)))
continue;
+ ref_paths[count++] = kstrdup(ce->path, GFP_ATOMIC);
+ }
+ }
- ses = find_ipc_from_server_path(sessions, ce->path);
- if (IS_ERR(ses))
- continue;
+out_unlock:
+ up_read(&htable_rw_lock);
- xid = get_xid();
- rc = get_dfs_referral(xid, ses, ce->path, &refs, &numrefs);
- free_xid(xid);
+ for (i = 0; i < count; i++) {
+ char *path = ref_paths[i];
+ struct dfs_info3_param *refs = NULL;
+ int numrefs = 0;
+ int rc = 0;
- if (!rc)
- update_cache_entry_locked(ce->path, refs, numrefs);
+ if (!path)
+ continue;
- free_dfs_info_array(refs, numrefs);
+ ses = find_ipc_from_server_path(sessions, path);
+ if (IS_ERR(ses))
+ goto next_referral;
+
+ xid = get_xid();
+ rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
+ free_xid(xid);
+
+ if (!rc) {
+ down_write(&htable_rw_lock);
+ ce = lookup_cache_entry(path);
+ /*
+ * We need to re-check it because other tasks might have it deleted or
+ * updated.
+ */
+ if (!IS_ERR(ce) && cache_entry_expired(ce))
+ update_cache_entry_locked(ce, refs, numrefs);
+ up_write(&htable_rw_lock);
}
+
+next_referral:
+ kfree(path);
+ free_dfs_info_array(refs, numrefs);
}
- up_write(&htable_rw_lock);
}
/*
--
2.32.0