On Tue, Sep 2, 2014 at 3:23 PM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> On Tue, Sep 02, 2014 at 01:58:58PM -0400, Trond Myklebust wrote:
>> This fixes an Oopsable race when starting up the callback server.
>>
>> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>> ---
>> fs/nfs/callback.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
>> index e3dd1cd175d9..b8fb3a4ef649 100644
>> --- a/fs/nfs/callback.c
>> +++ b/fs/nfs/callback.c
>> @@ -235,7 +235,7 @@ static int nfs_callback_start_svc(int minorversion, struct rpc_xprt *xprt,
>>
>> cb_info->serv = serv;
>> cb_info->rqst = rqstp;
>> - cb_info->task = kthread_run(callback_svc, cb_info->rqst,
>> + cb_info->task = kthread_create(callback_svc, cb_info->rqst,
>> "nfsv4.%u-svc", minorversion);
>> if (IS_ERR(cb_info->task)) {
>> ret = PTR_ERR(cb_info->task);
>> @@ -245,6 +245,7 @@ static int nfs_callback_start_svc(int minorversion, struct rpc_xprt *xprt,
>> return ret;
>> }
>> rqstp->rq_task = cb_info->task;
>> + wake_up_process(cb_info->task);
>
> Wouldn't it be cleaner to do something like:
>
> - cb_info->task = kthread_run(callback_svc, cb_info->rqst,
> + cb_info->task = rqstp->rq_run =
> + kthread_create(callback_svc, cb_info->rqst,
>
> or am I missing something subtile that the changelog didn't mention?
The above is fine if you call kthread_create(), but if you stick with
kthread_run(), then there is still the same atomicity issue that the
thread can be started before we've initialised cb_info->task and
rqstp->rq_run.
Internal testing has shown that this can lead to an oops when starting
lockd. I'm therefore assuming that the same thing can happen with the
NFS client callback channel.
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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