This is a note to let you know that I've just added the patch titled
cifs: Fix potential deadlock when updating vol in cifs_reconnect()
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cifs-fix-potential-deadlock-when-updating-vol-in-cifs_reconnect.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From stable-owner@xxxxxxxxxxxxxxx Fri Jun 23 23:35:43 2023
From: Rishabh Bhatnagar <risbhat@xxxxxxxxxx>
Date: Fri, 23 Jun 2023 21:34:06 +0000
Subject: cifs: Fix potential deadlock when updating vol in cifs_reconnect()
To: <gregkh@xxxxxxxxxxxxxxxxxxx>, <pc@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>, <linux-kernel@xxxxxxxxxxxxxxx>, <linux-cifs@xxxxxxxxxxxxxxx>, Steve French <stfrench@xxxxxxxxxxxxx>, "Rishabh Bhatnagar" <risbhat@xxxxxxxxxx>
Message-ID: <20230623213406.5596-6-risbhat@xxxxxxxxxx>
From: "Paulo Alcantara (SUSE)" <pc@xxxxxx>
commit 06d57378bcc9b2c33640945174842115593795d1 upstream.
We can't acquire volume lock while refreshing the DFS cache because
cifs_reconnect() may call dfs_cache_update_vol() while we are walking
through the volume list.
To prevent that, make vol_info refcounted, create a temp list with all
volumes eligible for refreshing, and then use it without any locks
held.
Besides, replace vol_lock with a spinlock and protect cache_ttl from
concurrent accesses or changes.
Signed-off-by: Paulo Alcantara (SUSE) <pc@xxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Rishabh Bhatnagar <risbhat@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/cifs/dfs_cache.c | 109 ++++++++++++++++++++++++++++++++++++----------------
1 file changed, 77 insertions(+), 32 deletions(-)
--- a/fs/cifs/dfs_cache.c
+++ b/fs/cifs/dfs_cache.c
@@ -49,15 +49,20 @@ struct cache_entry {
struct vol_info {
char *fullpath;
+ spinlock_t smb_vol_lock;
struct smb_vol smb_vol;
char *mntdata;
struct list_head list;
+ struct list_head rlist;
+ struct kref refcnt;
};
static struct kmem_cache *cache_slab __read_mostly;
static struct workqueue_struct *dfscache_wq __read_mostly;
static int cache_ttl;
+static DEFINE_SPINLOCK(cache_ttl_lock);
+
static struct nls_table *cache_nlsc;
/*
@@ -69,7 +74,7 @@ static struct hlist_head cache_htable[CA
static DEFINE_MUTEX(list_lock);
static LIST_HEAD(vol_list);
-static DEFINE_MUTEX(vol_lock);
+static DEFINE_SPINLOCK(vol_list_lock);
static void refresh_cache_worker(struct work_struct *work);
@@ -300,7 +305,6 @@ int dfs_cache_init(void)
for (i = 0; i < CACHE_HTABLE_SIZE; i++)
INIT_HLIST_HEAD(&cache_htable[i]);
- cache_ttl = -1;
cache_nlsc = load_nls_default();
cifs_dbg(FYI, "%s: initialized DFS referral cache\n", __func__);
@@ -471,15 +475,15 @@ add_cache_entry(unsigned int hash, const
hlist_add_head_rcu(&ce->hlist, &cache_htable[hash]);
- mutex_lock(&vol_lock);
- if (cache_ttl < 0) {
+ spin_lock(&cache_ttl_lock);
+ if (!cache_ttl) {
cache_ttl = ce->ttl;
queue_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
} else {
cache_ttl = min_t(int, cache_ttl, ce->ttl);
mod_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
}
- mutex_unlock(&vol_lock);
+ spin_unlock(&cache_ttl_lock);
return ce;
}
@@ -523,21 +527,32 @@ static inline void destroy_slab_cache(vo
kmem_cache_destroy(cache_slab);
}
-static inline void free_vol(struct vol_info *vi)
+static void __vol_release(struct vol_info *vi)
{
- list_del(&vi->list);
kfree(vi->fullpath);
kfree(vi->mntdata);
cifs_cleanup_volume_info_contents(&vi->smb_vol);
kfree(vi);
}
+static void vol_release(struct kref *kref)
+{
+ struct vol_info *vi = container_of(kref, struct vol_info, refcnt);
+
+ spin_lock(&vol_list_lock);
+ list_del(&vi->list);
+ spin_unlock(&vol_list_lock);
+ __vol_release(vi);
+}
+
static inline void free_vol_list(void)
{
struct vol_info *vi, *nvi;
- list_for_each_entry_safe(vi, nvi, &vol_list, list)
- free_vol(vi);
+ list_for_each_entry_safe(vi, nvi, &vol_list, list) {
+ list_del_init(&vi->list);
+ __vol_release(vi);
+ }
}
/**
@@ -1156,10 +1171,13 @@ int dfs_cache_add_vol(char *mntdata, str
goto err_free_fullpath;
vi->mntdata = mntdata;
+ spin_lock_init(&vi->smb_vol_lock);
+ kref_init(&vi->refcnt);
- mutex_lock(&vol_lock);
+ spin_lock(&vol_list_lock);
list_add_tail(&vi->list, &vol_list);
- mutex_unlock(&vol_lock);
+ spin_unlock(&vol_list_lock);
+
return 0;
err_free_fullpath:
@@ -1169,7 +1187,8 @@ err_free_vi:
return rc;
}
-static inline struct vol_info *find_vol(const char *fullpath)
+/* Must be called with vol_list_lock held */
+static struct vol_info *find_vol(const char *fullpath)
{
struct vol_info *vi;
@@ -1191,7 +1210,6 @@ static inline struct vol_info *find_vol(
*/
int dfs_cache_update_vol(const char *fullpath, struct TCP_Server_Info *server)
{
- int rc;
struct vol_info *vi;
if (!fullpath || !server)
@@ -1199,22 +1217,24 @@ int dfs_cache_update_vol(const char *ful
cifs_dbg(FYI, "%s: fullpath: %s\n", __func__, fullpath);
- mutex_lock(&vol_lock);
-
+ spin_lock(&vol_list_lock);
vi = find_vol(fullpath);
if (IS_ERR(vi)) {
- rc = PTR_ERR(vi);
- goto out;
+ spin_unlock(&vol_list_lock);
+ return PTR_ERR(vi);
}
+ kref_get(&vi->refcnt);
+ spin_unlock(&vol_list_lock);
cifs_dbg(FYI, "%s: updating volume info\n", __func__);
+ spin_lock(&vi->smb_vol_lock);
memcpy(&vi->smb_vol.dstaddr, &server->dstaddr,
sizeof(vi->smb_vol.dstaddr));
- rc = 0;
+ spin_unlock(&vi->smb_vol_lock);
-out:
- mutex_unlock(&vol_lock);
- return rc;
+ kref_put(&vi->refcnt, vol_release);
+
+ return 0;
}
/**
@@ -1231,11 +1251,11 @@ void dfs_cache_del_vol(const char *fullp
cifs_dbg(FYI, "%s: fullpath: %s\n", __func__, fullpath);
- mutex_lock(&vol_lock);
+ spin_lock(&vol_list_lock);
vi = find_vol(fullpath);
- if (!IS_ERR(vi))
- free_vol(vi);
- mutex_unlock(&vol_lock);
+ spin_unlock(&vol_list_lock);
+
+ kref_put(&vi->refcnt, vol_release);
}
/* Get all tcons that are within a DFS namespace and can be refreshed */
@@ -1449,27 +1469,52 @@ out:
*/
static void refresh_cache_worker(struct work_struct *work)
{
- struct vol_info *vi;
+ struct vol_info *vi, *nvi;
struct TCP_Server_Info *server;
- LIST_HEAD(list);
+ LIST_HEAD(vols);
+ LIST_HEAD(tcons);
struct cifs_tcon *tcon, *ntcon;
- mutex_lock(&vol_lock);
-
+ /*
+ * Find SMB volumes that are eligible (server->tcpStatus == CifsGood)
+ * for refreshing.
+ */
+ spin_lock(&vol_list_lock);
list_for_each_entry(vi, &vol_list, list) {
server = get_tcp_server(&vi->smb_vol);
if (!server)
continue;
- get_tcons(server, &list);
- list_for_each_entry_safe(tcon, ntcon, &list, ulist) {
+ kref_get(&vi->refcnt);
+ list_add_tail(&vi->rlist, &vols);
+ put_tcp_server(server);
+ }
+ spin_unlock(&vol_list_lock);
+
+ /* Walk through all TCONs and refresh any expired cache entry */
+ list_for_each_entry_safe(vi, nvi, &vols, rlist) {
+ spin_lock(&vi->smb_vol_lock);
+ server = get_tcp_server(&vi->smb_vol);
+ spin_unlock(&vi->smb_vol_lock);
+
+ if (!server)
+ goto next_vol;
+
+ get_tcons(server, &tcons);
+ list_for_each_entry_safe(tcon, ntcon, &tcons, ulist) {
refresh_tcon(vi, tcon);
list_del_init(&tcon->ulist);
cifs_put_tcon(tcon);
}
put_tcp_server(server);
+
+next_vol:
+ list_del_init(&vi->rlist);
+ kref_put(&vi->refcnt, vol_release);
}
+
+ spin_lock(&cache_ttl_lock);
queue_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
- mutex_unlock(&vol_lock);
+ spin_unlock(&cache_ttl_lock);
}
Patches currently in stable-queue which might be from stable-owner@xxxxxxxxxxxxxxx are
queue-5.4/cifs-clean-up-dfs-referral-cache.patch
queue-5.4/cifs-merge-is_path_valid-into-get_normalized_path.patch
queue-5.4/cifs-introduce-helpers-for-finding-tcp-connection.patch
queue-5.4/cifs-get-rid-of-kstrdup_const-d-paths.patch
queue-5.4/cifs-fix-potential-deadlock-when-updating-vol-in-cifs_reconnect.patch
