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SubjectRe: [PATCH v2 1/4] SUNRPC: release per-net clients lock before calling PipeFS dentries creation
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);


--
Best regards,
Stanislav Kinsbursky
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