On Tue, Sep 2, 2014 at 3:45 PM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote:
> On Tue, Sep 02, 2014 at 03:32:55PM -0400, Trond Myklebust wrote:
>> 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.
>
> The oops seen in practice were probably after applying 983c684466e0
> "SUNRPC: get rid of the request wait queue"?
>
> Though it was a bug before then too, of course.
>
Right. This is not needed until you merge the new sunrpc server
scalability stuff (which I'm assuming will be 3.18).
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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