diff mbox

[v2,1/4] SUNRPC: release per-net clients lock before calling PipeFS dentries creation

Message ID 20120227155055.7941.18741.stgit@localhost6.localdomain6
State Not Applicable, archived
Delegated to: David Miller
Headers show

Commit Message

Stanislav Kinsbursky Feb. 27, 2012, 3:50 p.m. UTC 
Lockdep is sad otherwise, because inode mutex is taken on PipeFS dentry
creation, which can be called on mount notification, where this per-net client
lock is taken on clients list walk.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>

---
 net/sunrpc/clnt.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)


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Comments

Stanislav Kinsbursky Feb. 27, 2012, 4:55 p.m. UTC | #1 
27.02.2012 20:21, Myklebust, Trond пишет:
> On Mon, 2012-02-27 at 19:50 +0400, Stanislav Kinsbursky wrote:
>> Lockdep is sad otherwise, because inode mutex is taken on PipeFS dentry
>> creation, which can be called on mount notification, where this per-net client
>> lock is taken on clients list walk.
>>
>> Signed-off-by: Stanislav Kinsbursky<skinsbursky@parallels.com>
>>
>> ---
>>   net/sunrpc/clnt.c |   10 +++++++---
>>   1 files changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
>> index bb7ed2f3..ddb5741 100644
>> --- a/net/sunrpc/clnt.c
>> +++ b/net/sunrpc/clnt.c
>> @@ -84,7 +84,7 @@ static void rpc_register_client(struct rpc_clnt *clnt)
>>   	struct sunrpc_net *sn = net_generic(clnt->cl_xprt->xprt_net, sunrpc_net_id);
>>
>>   	spin_lock(&sn->rpc_client_lock);
>> -	list_add(&clnt->cl_clients,&sn->all_clients);
>> +	list_add_tail(&clnt->cl_clients,&sn->all_clients);
>>   	spin_unlock(&sn->rpc_client_lock);
>>   }
>>
>> @@ -208,15 +208,19 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
>>   			    void *ptr)
>>   {
>>   	struct super_block *sb = ptr;
>> -	struct rpc_clnt *clnt;
>> +	struct rpc_clnt *clnt, *tmp;
>>   	int error = 0;
>>   	struct sunrpc_net *sn = net_generic(sb->s_fs_info, sunrpc_net_id);
>>
>>   	spin_lock(&sn->rpc_client_lock);
>> -	list_for_each_entry(clnt,&sn->all_clients, cl_clients) {
>> +	list_for_each_entry_safe(clnt, tmp,&sn->all_clients, cl_clients) {
>> +		atomic_inc(&clnt->cl_count);
>> +		spin_unlock(&sn->rpc_client_lock);
>>   		error = __rpc_pipefs_event(clnt, event, sb);
>> +		rpc_release_client(clnt);
>>   		if (error)
>>   			break;
>> +		spin_lock(&sn->rpc_client_lock);
>>   	}
>>   	spin_unlock(&sn->rpc_client_lock);
>>   	return error;
>>
>
> This won't be safe. Nothing guarantees that 'tmp' remains valid after
> you drop the spin_lock.
>
> I think you rather need to add a check for whether clnt->cl_dentry is in
> the right state (NULL if RPC_PIPEFS_UMOUNT or non-NULL if
> RPC_PIPEFS_MOUNT) before deciding whether or not to atomic_inc() and
> drop the lock, so that you can restart the loop after calling
> __rpc_pipefs_event().
>

Gmmm.
Please, correct me, if I'm wrong, that you are proposing something like this:

   	spin_lock(&sn->rpc_client_lock);
again:
	list_for_each_entry(clnt,&sn->all_clients, cl_clients) {
		if ((event == RPC_PIPEFS_MOUNT) && clnt->cl_dentry) ||
		    (event == RPC_PIPEFS_UMOUNT) && !clnt->cl_dentry))
			continue;
		atomic_inc(&clnt->cl_count);
		spin_unlock(&sn->rpc_client_lock);
    		error = __rpc_pipefs_event(clnt, event, sb);
		rpc_release_client(clnt);
		spin_lock(&sn->rpc_client_lock);
    		if (error)
    			break;
		goto again;
    	}
    	spin_unlock(&sn->rpc_client_lock);
David Laight Feb. 27, 2012, 5:11 p.m. UTC | #2 
> Gmmm.
> Please, correct me, if I'm wrong, that you are proposing 
> something like this:
> 
>    	spin_lock(&sn->rpc_client_lock);
> again:
> 	list_for_each_entry(clnt,&sn->all_clients, cl_clients) {
> 		if ((event == RPC_PIPEFS_MOUNT) && clnt->cl_dentry) ||
> 		    (event == RPC_PIPEFS_UMOUNT) && !clnt->cl_dentry))
> 			continue;
> 		atomic_inc(&clnt->cl_count);
> 		spin_unlock(&sn->rpc_client_lock);
>     		error = __rpc_pipefs_event(clnt, event, sb);
> 		rpc_release_client(clnt);
> 		spin_lock(&sn->rpc_client_lock);
>     		if (error)
>     			break;
> 		goto again;
>     	}
>     	spin_unlock(&sn->rpc_client_lock);

You might manage to request reference to the 'next'
item while holding the lock. So maybe a loop that has:

	error = ...
	if (error) {
		rpc_release_client(clnt);
		break;
	}
	spin_lock(&sn->rpc_client_lock);
	next_clnt = list_next(clnt);
	if (next_clnt)
		atomic_inc(&next_clnt->cl_count);
	spin_unlock(&sn->rpc_client_lock);
	rpc_release_client(clnt);
	clnt = next_clnt;
   } while (clnt != NULL);

	David


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Trond Myklebust Feb. 27, 2012, 5:37 p.m. UTC | #3 
On Mon, 2012-02-27 at 20:55 +0400, Stanislav Kinsbursky wrote:
> 27.02.2012 20:21, Myklebust, Trond пишет:

> > On Mon, 2012-02-27 at 19:50 +0400, Stanislav Kinsbursky wrote:

> >> Lockdep is sad otherwise, because inode mutex is taken on PipeFS dentry

> >> creation, which can be called on mount notification, where this per-net client

> >> lock is taken on clients list walk.

> >>

> >> Signed-off-by: Stanislav Kinsbursky<skinsbursky@parallels.com>

> >>

> >> ---

> >>   net/sunrpc/clnt.c |   10 +++++++---

> >>   1 files changed, 7 insertions(+), 3 deletions(-)

> >>

> >> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c

> >> index bb7ed2f3..ddb5741 100644

> >> --- a/net/sunrpc/clnt.c

> >> +++ b/net/sunrpc/clnt.c

> >> @@ -84,7 +84,7 @@ static void rpc_register_client(struct rpc_clnt *clnt)

> >>   	struct sunrpc_net *sn = net_generic(clnt->cl_xprt->xprt_net, sunrpc_net_id);

> >>

> >>   	spin_lock(&sn->rpc_client_lock);

> >> -	list_add(&clnt->cl_clients,&sn->all_clients);

> >> +	list_add_tail(&clnt->cl_clients,&sn->all_clients);

> >>   	spin_unlock(&sn->rpc_client_lock);

> >>   }

> >>

> >> @@ -208,15 +208,19 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,

> >>   			    void *ptr)

> >>   {

> >>   	struct super_block *sb = ptr;

> >> -	struct rpc_clnt *clnt;

> >> +	struct rpc_clnt *clnt, *tmp;

> >>   	int error = 0;

> >>   	struct sunrpc_net *sn = net_generic(sb->s_fs_info, sunrpc_net_id);

> >>

> >>   	spin_lock(&sn->rpc_client_lock);

> >> -	list_for_each_entry(clnt,&sn->all_clients, cl_clients) {

> >> +	list_for_each_entry_safe(clnt, tmp,&sn->all_clients, cl_clients) {

> >> +		atomic_inc(&clnt->cl_count);

> >> +		spin_unlock(&sn->rpc_client_lock);

> >>   		error = __rpc_pipefs_event(clnt, event, sb);

> >> +		rpc_release_client(clnt);

> >>   		if (error)

> >>   			break;

> >> +		spin_lock(&sn->rpc_client_lock);

> >>   	}

> >>   	spin_unlock(&sn->rpc_client_lock);

> >>   	return error;

> >>

> >

> > This won't be safe. Nothing guarantees that 'tmp' remains valid after

> > you drop the spin_lock.

> >

> > I think you rather need to add a check for whether clnt->cl_dentry is in

> > the right state (NULL if RPC_PIPEFS_UMOUNT or non-NULL if

> > RPC_PIPEFS_MOUNT) before deciding whether or not to atomic_inc() and

> > drop the lock, so that you can restart the loop after calling

> > __rpc_pipefs_event().

> >

> 

> Gmmm.

> Please, correct me, if I'm wrong, that you are proposing something like this:

> 

>    	spin_lock(&sn->rpc_client_lock);

> again:

> 	list_for_each_entry(clnt,&sn->all_clients, cl_clients) {

> 		if ((event == RPC_PIPEFS_MOUNT) && clnt->cl_dentry) ||

> 		    (event == RPC_PIPEFS_UMOUNT) && !clnt->cl_dentry))

> 			continue;

> 		atomic_inc(&clnt->cl_count);

> 		spin_unlock(&sn->rpc_client_lock);

>     		error = __rpc_pipefs_event(clnt, event, sb);

> 		rpc_release_client(clnt);

> 		spin_lock(&sn->rpc_client_lock);

>     		if (error)

>     			break;

> 		goto again;

>     	}

>     	spin_unlock(&sn->rpc_client_lock);


Something along those lines, yes... Alternatively, you could do as David
proposes, and grab a reference to the next rpc_client before calling
rpc_release_client. Either works for me...

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com
diff mbox

Patch

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index bb7ed2f3..ddb5741 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -84,7 +84,7 @@  static void rpc_register_client(struct rpc_clnt *clnt)
 	struct sunrpc_net *sn = net_generic(clnt->cl_xprt->xprt_net, sunrpc_net_id);
 
 	spin_lock(&sn->rpc_client_lock);
-	list_add(&clnt->cl_clients, &sn->all_clients);
+	list_add_tail(&clnt->cl_clients, &sn->all_clients);
 	spin_unlock(&sn->rpc_client_lock);
 }
 
@@ -208,15 +208,19 @@  static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
 			    void *ptr)
 {
 	struct super_block *sb = ptr;
-	struct rpc_clnt *clnt;
+	struct rpc_clnt *clnt, *tmp;
 	int error = 0;
 	struct sunrpc_net *sn = net_generic(sb->s_fs_info, sunrpc_net_id);
 
 	spin_lock(&sn->rpc_client_lock);
-	list_for_each_entry(clnt, &sn->all_clients, cl_clients) {
+	list_for_each_entry_safe(clnt, tmp, &sn->all_clients, cl_clients) {
+		atomic_inc(&clnt->cl_count);
+		spin_unlock(&sn->rpc_client_lock);
 		error = __rpc_pipefs_event(clnt, event, sb);
+		rpc_release_client(clnt);
 		if (error)
 			break;
+		spin_lock(&sn->rpc_client_lock);
 	}
 	spin_unlock(&sn->rpc_client_lock);
 	return error;