> On Jan 10, 2023, at 12:33 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
>
>
> On 1/10/23 2:30 AM, Jeff Layton wrote:
>> On Mon, 2023-01-09 at 22:48 -0800, Dai Ngo wrote:
>>> Currently nfsd4_state_shrinker_worker can be schduled multiple times
>>> from nfsd4_state_shrinker_count when memory is low. This causes
>>> the WARN_ON_ONCE in __queue_delayed_work to trigger.
>>>
>>> This patch allows only one instance of nfsd4_state_shrinker_worker
>>> at a time using the nfsd_shrinker_active flag, protected by the
>>> client_lock.
>>>
>>> Replace mod_delayed_work with queue_delayed_work since we
>>> don't expect to modify the delay of any pending work.
>>>
>>> Fixes: 44df6f439a17 ("NFSD: add delegation reaper to react to low memory condition")
>>> Reported-by: Mike Galbraith <efault@xxxxxx>
>>> Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
>>> ---
>>> fs/nfsd/netns.h | 1 +
>>> fs/nfsd/nfs4state.c | 16 ++++++++++++++--
>>> 2 files changed, 15 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
>>> index 8c854ba3285b..801d70926442 100644
>>> --- a/fs/nfsd/netns.h
>>> +++ b/fs/nfsd/netns.h
>>> @@ -196,6 +196,7 @@ struct nfsd_net {
>>> atomic_t nfsd_courtesy_clients;
>>> struct shrinker nfsd_client_shrinker;
>>> struct delayed_work nfsd_shrinker_work;
>>> + bool nfsd_shrinker_active;
>>> };
>>> /* Simple check to find out if a given net was properly initialized */
>>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>>> index ee56c9466304..e00551af6a11 100644
>>> --- a/fs/nfsd/nfs4state.c
>>> +++ b/fs/nfsd/nfs4state.c
>>> @@ -4407,11 +4407,20 @@ nfsd4_state_shrinker_count(struct shrinker *shrink, struct shrink_control *sc)
>>> struct nfsd_net *nn = container_of(shrink,
>>> struct nfsd_net, nfsd_client_shrinker);
>>> + spin_lock(&nn->client_lock);
>>> + if (nn->nfsd_shrinker_active) {
>>> + spin_unlock(&nn->client_lock);
>>> + return 0;
>>> + }
>> Is this extra machinery really necessary? The bool and spinlock don't
>> seem to be needed. Typically there is no issue with calling
>> queued_delayed_work when the work is already queued. It just returns
>> false in that case without doing anything.
>
> When there are multiple calls to mod_delayed_work/queue_delayed_work
> we hit the WARN_ON_ONCE's in __queue_delayed_work and __queue_work if
> the work is queued but not execute yet.
The delay argument of zero is interesting. If it's set to a value
greater than zero, do you still see a problem?
> This problem was reported by Mike. I initially tried with only the
> bool but that was not enough that was why the spinlock was added.
> Mike verified that the patch fixed the problem.
>
> -Dai
>
>>
>>> count = atomic_read(&nn->nfsd_courtesy_clients);
>>> if (!count)
>>> count = atomic_long_read(&num_delegations);
>>> - if (count)
>>> - mod_delayed_work(laundry_wq, &nn->nfsd_shrinker_work, 0);
>>> + if (count) {
>>> + nn->nfsd_shrinker_active = true;
>>> + spin_unlock(&nn->client_lock);
>>> + queue_delayed_work(laundry_wq, &nn->nfsd_shrinker_work, 0);
>>> + } else
>>> + spin_unlock(&nn->client_lock);
>>> return (unsigned long)count;
>>> }
>>> @@ -6239,6 +6248,9 @@ nfsd4_state_shrinker_worker(struct work_struct *work)
>>> courtesy_client_reaper(nn);
>>> deleg_reaper(nn);
>>> + spin_lock(&nn->client_lock);
>>> + nn->nfsd_shrinker_active = 0;
>>> + spin_unlock(&nn->client_lock);
>>> }
>>> static inline __be32 nfs4_check_fh(struct svc_fh *fhp, struct nfs4_stid *stp)
--
Chuck Lever
