Re: [PATCH 0/5 v2] sunrpc: stop refcounting svc_serv

Chuck Lever III
2023-12-15T14:38:57Z

> On Dec 15, 2023, at 9:26 AM, Jeff Layton <jlayton@kernel.org> wrote:
>
> On Fri, 2023-12-15 at 14:19 +0000, Chuck Lever III wrote:
>>> On Dec 15, 2023, at 5:59 AM, Jeff Layton <jlayton@kernel.org> wrote:
>>>
>>> On Fri, 2023-12-15 at 11:56 +1100, NeilBrown wrote:
>>>> I sent an earlier version of this series, got some feed back, revised
>>>> it, but never sent it again. Sorry.
>>>>
>>>> The main feedback was around the interaction between sunrpc and nfsd for
>>>> handling poolstats. I have changed that so that nfsd tells sunrpc where
>>>> the svc_serv pointer lives, and where to find a mutex to protect it.
>>>> sunrpc then taks the mutex and accesses the pointer - if not NULL. I
>>>> think this is nicer than the version that pass around funciton pointers.
>>>>
>>>> This series is against nfsd-next
>>>>
>>>> Thanks,
>>>> NeilBrown
>>>>
>>>>
>>>> [PATCH 1/5] nfsd: call nfsd_last_thread() before final nfsd_put()
>>>> [PATCH 2/5] svc: don't hold reference for poolstats, only mutex.
>>>> [PATCH 3/5] nfsd: hold nfsd_mutex across entire netlink operation
>>>> [PATCH 4/5] SUNRPC: discard sv_refcnt, and svc_get/svc_put
>>>> [PATCH 5/5] nfsd: rename nfsd_last_thread() to nfsd_destroy_serv()
>>>
>>> I'm not sure patch #2 is better than the version with function pointers,
>>> but it seems reasonable.
>>>
>>> Note that patch #1 probably needs to go to v6.6 stable, and I think we
>>> want #3 in v6.7 before it ships.
>>
>> Remind me why #3 should go into v6.7-rc ? There's no Fixes tag on
>> that one.
>>
>>
>
> It's the problem I noted to Lorenzo the other day:
>
>
> https://lore.kernel.org/linux-nfs/5d9bbb599569ce29f16e4e0eef6b291eda0f375b.camel@kernel.org/T/#u
>
> Once you've dropped the nfsd_mutex, there is no guarantee that
> nn->nfsd_serv will still be a valid pointer. Holding the mutex across
> the operation (like Neil's patch does), should close the race.

OK. I'll add:

Fixes: bd9d6a3efa97 ("NFSD: add rpc_status netlink support")

I will apply 1/3 and 3/3 to v6.7-rc, and the others will go to
v6.8 (nfsd-next) once it is rebased on v6.7-rc7.

--
Chuck Lever