On 1/11/23 2:47 AM, Jeff Layton wrote:

On Wed, 2023-01-11 at 02:24 -0800, Dai Ngo wrote:

quoted

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 <redacted>
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
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.

Agreed. We need to get to the bottom of this.

-Dai

quoted

  	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);