[Devel] [PATCH] nfs: protect callback execution against per-net callback thread shutdown

[Stanislav Kinsburskiy]

Well... Maybe.
Let's check, how it works with our kernel.

07.11.2017 10:16, Konstantin Khorenko пишет:
> Going to send it to mainstream as well?
> 
> -- 
> Best regards,
> 
> Konstantin Khorenko,
> Virtuozzo Linux Kernel Team
> 
> On 11/03/2017 07:47 PM, Stanislav Kinsburskiy wrote:
>> From: Stanislav Kinsburskiy <skinsbursky at parallels.com>
>>
>> The problem is that per-net SUNRPC transports shutdown is done regardless
>> current callback execution. This is a race leading to transport use-after-free
>> in callback handler.
>> This patch fixes it in stright-forward way. I.e. it protects callback
>> execution with the same mutex used for per-net data creation and destruction.
>> Hopefully, it won't slow down NFS client significantly.
>>
>> https://jira.sw.ru/browse/PSBM-75751
>>
>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at parallels.com>
>> ---
>>  fs/nfs/callback.c |    3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
>> index 0beb275..82e8ed1 100644
>> --- a/fs/nfs/callback.c
>> +++ b/fs/nfs/callback.c
>> @@ -118,6 +118,7 @@ nfs41_callback_svc(void *vrqstp)
>>              continue;
>>
>>          prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
>> +        mutex_lock(&nfs_callback_mutex);
>>          spin_lock_bh(&serv->sv_cb_lock);
>>          if (!list_empty(&serv->sv_cb_list)) {
>>              req = list_first_entry(&serv->sv_cb_list,
>> @@ -129,8 +130,10 @@ nfs41_callback_svc(void *vrqstp)
>>              error = bc_svc_process(serv, req, rqstp);
>>              dprintk("bc_svc_process() returned w/ error code= %d\n",
>>                  error);
>> +            mutex_unlock(&nfs_callback_mutex);
>>          } else {
>>              spin_unlock_bh(&serv->sv_cb_lock);
>> +            mutex_unlock(&nfs_callback_mutex);
>>              schedule();
>>              finish_wait(&serv->sv_cb_waitq, &wq);
>>          }
>>
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