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

Chuck Lever III
2023-12-15T15:38:19Z

> On Dec 15, 2023, at 9:38 AM, Chuck Lever III <chuck.lever@oracle.com> wrote:
>
>> 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.

Please check the two patches at the tip of the nfsd-fixes
branch here:

https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git

I plan to apply the other three in this series to nfsd-next.

--
Chuck Lever