On Wed, 2023-01-11 at 02:24 -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.
>
> Change nfsd_shrinker_work from delayed_work to work_struct since we
> don't use the delay.
>
> Replace mod_delayed_work in nfsd4_state_shrinker_count with queue_work.
>
> Cancel work_struct nfsd_shrinker_work after unregistering shrinker
> in nfs4_state_shutdown_net
>
> 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>
> ---
> v2:
> . Change nfsd_shrinker_work from delayed_work to work_struct
> . Replace mod_delayed_work in nfsd4_state_shrinker_count with queue_work
> . Cancel work_struct nfsd_shrinker_work after unregistering shrinker
> v3:
> . set nfsd_shrinker_active earlier in nfsd4_state_shrinker_count
>
> fs/nfsd/netns.h | 3 ++-
> fs/nfsd/nfs4state.c | 24 +++++++++++++++++++-----
> 2 files changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index 8c854ba3285b..b0c7b657324b 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -195,7 +195,8 @@ struct nfsd_net {
>
> atomic_t nfsd_courtesy_clients;
> struct shrinker nfsd_client_shrinker;
> - struct delayed_work nfsd_shrinker_work;
> + struct work_struct 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 a7cfefd7c205..35ec4cba88b3 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -4407,11 +4407,22 @@ 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;
> + }
> + nn->nfsd_shrinker_active = true;
> 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) {
> + spin_unlock(&nn->client_lock);
> + queue_work(laundry_wq, &nn->nfsd_shrinker_work);
> + } else {
> + nn->nfsd_shrinker_active = false;
> + spin_unlock(&nn->client_lock);
> + }
The change to normal work_struct is an improvement, but NAK on this
patch. The spinlocking and flag are not needed here. I seriously doubt
that we have a clear understanding of this problem.
> return (unsigned long)count;
> }
>
> @@ -6233,12 +6244,14 @@ deleg_reaper(struct nfsd_net *nn)
> static void
> nfsd4_state_shrinker_worker(struct work_struct *work)
> {
> - struct delayed_work *dwork = to_delayed_work(work);
> - struct nfsd_net *nn = container_of(dwork, struct nfsd_net,
> + struct nfsd_net *nn = container_of(work, struct nfsd_net,
> nfsd_shrinker_work);
>
> courtesy_client_reaper(nn);
> deleg_reaper(nn);
> + spin_lock(&nn->client_lock);
> + nn->nfsd_shrinker_active = false;
> + spin_unlock(&nn->client_lock);
> }
>
> static inline __be32 nfs4_check_fh(struct svc_fh *fhp, struct nfs4_stid *stp)
> @@ -8064,7 +8077,7 @@ static int nfs4_state_create_net(struct net *net)
> INIT_LIST_HEAD(&nn->blocked_locks_lru);
>
> INIT_DELAYED_WORK(&nn->laundromat_work, laundromat_main);
> - INIT_DELAYED_WORK(&nn->nfsd_shrinker_work, nfsd4_state_shrinker_worker);
> + INIT_WORK(&nn->nfsd_shrinker_work, nfsd4_state_shrinker_worker);
> get_net(net);
>
> nn->nfsd_client_shrinker.scan_objects = nfsd4_state_shrinker_scan;
> @@ -8171,6 +8184,7 @@ nfs4_state_shutdown_net(struct net *net)
> struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>
> unregister_shrinker(&nn->nfsd_client_shrinker);
> + cancel_work(&nn->nfsd_shrinker_work);
> cancel_delayed_work_sync(&nn->laundromat_work);
> locks_end_grace(&nn->nfsd4_manager);
>
--
Jeff Layton <jlayton@xxxxxxxxxx>
