diff mbox

[v3,2/4] SUNRPC: fix races on PipeFS UMOUNT notifications

Message ID 20130624075245.17104.6279.stgit@localhost.localdomain (mailing list archive)
State New, archived
Headers show

Commit Message

Stanislav Kinsbursky June 24, 2013, 7:52 a.m. UTC 
CPU#0                                   CPU#1
-----------------------------           -----------------------------
rpc_kill_sb
sn->pipefs_sb = NULL                    rpc_release_client
(UMOUNT_EVENT)                          rpc_free_auth
rpc_pipefs_event
rpc_get_client_for_event
!atomic_inc_not_zero(cl_count)
<skip the client>
                                        atomic_inc(cl_count)
                                        rpc_free_client
                                        rpc_clnt_remove_pipedir
                                        <skip client dir removing>

To fix this, this patch does the following:

1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
2) Removes SUNRPC client from the list AFTER pipes destroying.
3) Doesn't hold RPC client on notification: if client in the list, then it
can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: stable@vger.kernel.org
---
 net/sunrpc/clnt.c     |    5 +----
 net/sunrpc/rpc_pipe.c |    2 +-
 2 files changed, 2 insertions(+), 5 deletions(-)


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Comments

Trond Myklebust June 25, 2013, 4:13 p.m. UTC | #1 
On Mon, 2013-06-24 at 11:52 +0400, Stanislav Kinsbursky wrote:
> CPU#0                                   CPU#1
> -----------------------------           -----------------------------
> rpc_kill_sb
> sn->pipefs_sb = NULL                    rpc_release_client
> (UMOUNT_EVENT)                          rpc_free_auth
> rpc_pipefs_event
> rpc_get_client_for_event
> !atomic_inc_not_zero(cl_count)
> <skip the client>
>                                         atomic_inc(cl_count)
>                                         rpc_free_client
>                                         rpc_clnt_remove_pipedir
>                                         <skip client dir removing>
> 
> To fix this, this patch does the following:
> 
> 1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
> 2) Removes SUNRPC client from the list AFTER pipes destroying.
> 3) Doesn't hold RPC client on notification: if client in the list, then it
> can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
> Cc: stable@vger.kernel.org
> ---
>  net/sunrpc/clnt.c     |    5 +----
>  net/sunrpc/rpc_pipe.c |    2 +-
>  2 files changed, 2 insertions(+), 5 deletions(-)

<snip>

> diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
> index c512448..efca2f7 100644
> --- a/net/sunrpc/rpc_pipe.c
> +++ b/net/sunrpc/rpc_pipe.c
> @@ -1165,7 +1165,6 @@ static void rpc_kill_sb(struct super_block *sb)
>  		goto out;
>  	}
>  	sn->pipefs_sb = NULL;
> -	mutex_unlock(&sn->pipefs_sb_lock);
>  	dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
>  		net, NET_NAME(net));
>  	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
> @@ -1173,6 +1172,7 @@ static void rpc_kill_sb(struct super_block *sb)
>  					   sb);
>  	put_net(net);
>  out:
> +	mutex_unlock(&sn->pipefs_sb_lock);

Is this safe to do after the put_net()?

>  	kill_litter_super(sb);
>  }
>  
>
Stanislav Kinsbursky June 26, 2013, 5:32 a.m. UTC | #2 
25.06.2013 20:13, Myklebust, Trond ?????:
> On Mon, 2013-06-24 at 11:52 +0400, Stanislav Kinsbursky wrote:
>> CPU#0                                   CPU#1
>> -----------------------------           -----------------------------
>> rpc_kill_sb
>> sn->pipefs_sb = NULL                    rpc_release_client
>> (UMOUNT_EVENT)                          rpc_free_auth
>> rpc_pipefs_event
>> rpc_get_client_for_event
>> !atomic_inc_not_zero(cl_count)
>> <skip the client>
>>                                          atomic_inc(cl_count)
>>                                          rpc_free_client
>>                                          rpc_clnt_remove_pipedir
>>                                          <skip client dir removing>
>>
>> To fix this, this patch does the following:
>>
>> 1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
>> 2) Removes SUNRPC client from the list AFTER pipes destroying.
>> 3) Doesn't hold RPC client on notification: if client in the list, then it
>> can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.
>>
>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
>> Cc: stable@vger.kernel.org
>> ---
>>   net/sunrpc/clnt.c     |    5 +----
>>   net/sunrpc/rpc_pipe.c |    2 +-
>>   2 files changed, 2 insertions(+), 5 deletions(-)
>
> <snip>
>
>> diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
>> index c512448..efca2f7 100644
>> --- a/net/sunrpc/rpc_pipe.c
>> +++ b/net/sunrpc/rpc_pipe.c
>> @@ -1165,7 +1165,6 @@ static void rpc_kill_sb(struct super_block *sb)
>>   		goto out;
>>   	}
>>   	sn->pipefs_sb = NULL;
>> -	mutex_unlock(&sn->pipefs_sb_lock);
>>   	dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
>>   		net, NET_NAME(net));
>>   	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
>> @@ -1173,6 +1172,7 @@ static void rpc_kill_sb(struct super_block *sb)
>>   					   sb);
>>   	put_net(net);
>>   out:
>> +	mutex_unlock(&sn->pipefs_sb_lock);
>
> Is this safe to do after the put_net()?
>

Sure it's not. Sorry.
Will send the patch once more.

>>   	kill_litter_super(sb);
>>   }
>>
>>
>
>
diff mbox

Patch

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index b827a4b..41f180c 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -236,8 +236,6 @@  static struct rpc_clnt *rpc_get_client_for_event(struct net *net, int event)
 			continue;
 		if (rpc_clnt_skip_event(clnt, event))
 			continue;
-		if (atomic_inc_not_zero(&clnt->cl_count) == 0)
-			continue;
 		spin_unlock(&sn->rpc_client_lock);
 		return clnt;
 	}
@@ -254,7 +252,6 @@  static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
 
 	while ((clnt = rpc_get_client_for_event(sb->s_fs_info, event))) {
 		error = __rpc_pipefs_event(clnt, event, sb);
-		rpc_release_client(clnt);
 		if (error)
 			break;
 	}
@@ -641,8 +638,8 @@  rpc_free_client(struct rpc_clnt *clnt)
 			rcu_dereference(clnt->cl_xprt)->servername);
 	if (clnt->cl_parent != clnt)
 		rpc_release_client(clnt->cl_parent);
-	rpc_unregister_client(clnt);
 	rpc_clnt_remove_pipedir(clnt);
+	rpc_unregister_client(clnt);
 	rpc_free_iostats(clnt->cl_metrics);
 	kfree(clnt->cl_principal);
 	clnt->cl_metrics = NULL;
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index c512448..efca2f7 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -1165,7 +1165,6 @@  static void rpc_kill_sb(struct super_block *sb)
 		goto out;
 	}
 	sn->pipefs_sb = NULL;
-	mutex_unlock(&sn->pipefs_sb_lock);
 	dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
 		net, NET_NAME(net));
 	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
@@ -1173,6 +1172,7 @@  static void rpc_kill_sb(struct super_block *sb)
 					   sb);
 	put_net(net);
 out:
+	mutex_unlock(&sn->pipefs_sb_lock);
 	kill_litter_super(sb);
 }