> On Jan 5, 2023, at 3:43 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> On Thu, 2023-01-05 at 14:46 +0000, Chuck Lever III wrote:
>>
>>> On Jan 5, 2023, at 7:18 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>>>
>>> Even though there is a WARN_ON_ONCE check, it seems possible for
>>> nfs4_find_file to race with the destruction of an fi_deleg_file while
>>> trying to take a reference to it.
>>>
>>> put_deleg_file is done while holding the fi_lock. Take and hold it
>>> when dealing with the fi_deleg_file in nfs4_find_file.
>>>
>>> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
>>> ---
>>> fs/nfsd/nfs4state.c | 16 ++++++++++------
>>> 1 file changed, 10 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>>> index b68238024e49..3df3ae84bd07 100644
>>> --- a/fs/nfsd/nfs4state.c
>>> +++ b/fs/nfsd/nfs4state.c
>>> @@ -6417,23 +6417,27 @@ nfsd4_lookup_stateid(struct nfsd4_compound_state *cstate,
>>> static struct nfsd_file *
>>> nfs4_find_file(struct nfs4_stid *s, int flags)
>>> {
>>> + struct nfsd_file *ret = NULL;
>>> +
>>> if (!s)
>>> return NULL;
>>>
>>> switch (s->sc_type) {
>>> case NFS4_DELEG_STID:
>>> - if (WARN_ON_ONCE(!s->sc_file->fi_deleg_file))
>>> - return NULL;
>>> - return nfsd_file_get(s->sc_file->fi_deleg_file);
>>> + spin_lock(&s->sc_file->fi_lock);
>>> + if (!WARN_ON_ONCE(!s->sc_file->fi_deleg_file))
>>
>> You'd think this would be a really really hard race to hit.
>>
>> What I'm wondering, though, is whether the WARN_ON_ONCE should
>> be dropped by this patch. I've never seen it fire.
>>
>>
>
> I have:
>
> https://bugzilla.redhat.com/show_bug.cgi?id=1997177
> It's possible though that those WARNs are fallout from other bugs in the
> delegation handling, but it's hard to know for sure.
Before 2015 there were a bunch of BUG_ON's in this code that
were converted to WARN after Linus complained. Before that,
I think these were all debugging sentinels. (in which case
I would argue they might be better recast as tracepoints,
but that's for another day).
> I think we ought to keep it there for now.
The question is whether the WARN_ON is adding value for customers.
Can they do something about it? If they give us this information,
can we do something about it?
I can't tell from the warning whether the problem is due to a
server bug or valid client behavior. Both the server and the
client workload appear to survive.
So, I just don't feel like it's adding value, and firing a WARN
while holding a spinlock makes me squidgy.
>>> + ret = nfsd_file_get(s->sc_file->fi_deleg_file);
>>> + spin_unlock(&s->sc_file->fi_lock);
>>> + break;
>>> case NFS4_OPEN_STID:
>>> case NFS4_LOCK_STID:
>>> if (flags & RD_STATE)
>>> - return find_readable_file(s->sc_file);
>>> + ret = find_readable_file(s->sc_file);
>>> else
>>> - return find_writeable_file(s->sc_file);
>>> + ret = find_writeable_file(s->sc_file);
>>> }
>>>
>>> - return NULL;
>>> + return ret;
>>> }
>>>
>>> static __be32
>>> --
>>> 2.39.0
>>>
>>
>> --
>> Chuck Lever
>>
>>
>>
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
--
Chuck Lever
