Re: [PATCH 1/2] nfsd: use new wake_up_var interfaces.

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2024-12-06 at 13:55 +1100, NeilBrown wrote:
> The wake_up_var interface is fragile as barriers are sometimes needed.
> There are now new interfaces so that most wake-ups can use an interface
> that is guaranteed to have all barriers needed.
> 
> This patch changes the wake up on cl_cb_inflight to use
> atomic_dec_and_wake_up().
> 
> It also changes the wake up on rp_locked to use store_release_wake_up().
> This involves changing rp_locked from atomic_t to int.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
>  fs/nfsd/nfs4callback.c |  3 +--
>  fs/nfsd/nfs4state.c    | 16 ++++++----------
>  fs/nfsd/state.h        |  2 +-
>  3 files changed, 8 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
> index 3877b53e429f..a8dc9de2f7fb 100644
> --- a/fs/nfsd/nfs4callback.c
> +++ b/fs/nfsd/nfs4callback.c
> @@ -1036,8 +1036,7 @@ static void nfsd41_cb_inflight_begin(struct nfs4_client *clp)
>  static void nfsd41_cb_inflight_end(struct nfs4_client *clp)
>  {
>  
> -	if (atomic_dec_and_test(&clp->cl_cb_inflight))
> -		wake_up_var(&clp->cl_cb_inflight);
> +	atomic_dec_and_wake_up(&clp->cl_cb_inflight);
>  }
>  
>  static void nfsd41_cb_inflight_wait_complete(struct nfs4_client *clp)
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 741b9449f727..9fbf7c8f0a3e 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -4739,7 +4739,7 @@ static void init_nfs4_replay(struct nfs4_replay *rp)
>  	rp->rp_status = nfserr_serverfault;
>  	rp->rp_buflen = 0;
>  	rp->rp_buf = rp->rp_ibuf;
> -	atomic_set(&rp->rp_locked, RP_UNLOCKED);
> +	rp->rp_locked = RP_UNLOCKED;
>  }
>  
>  static int nfsd4_cstate_assign_replay(struct nfsd4_compound_state *cstate,
> @@ -4747,9 +4747,9 @@ static int nfsd4_cstate_assign_replay(struct nfsd4_compound_state *cstate,
>  {
>  	if (!nfsd4_has_session(cstate)) {
>  		wait_var_event(&so->so_replay.rp_locked,
> -			       atomic_cmpxchg(&so->so_replay.rp_locked,
> -					      RP_UNLOCKED, RP_LOCKED) != RP_LOCKED);
> -		if (atomic_read(&so->so_replay.rp_locked) == RP_UNHASHED)
> +			       cmpxchg(&so->so_replay.rp_locked,
> +				       RP_UNLOCKED, RP_LOCKED) != RP_LOCKED);

nit: try_cmpxchg() generates more efficient assembly. Can we switch to
that here too?

> +		if (so->so_replay.rp_locked == RP_UNHASHED)
>  			return -EAGAIN;
>  		cstate->replay_owner = nfs4_get_stateowner(so);
>  	}
> @@ -4762,9 +4762,7 @@ void nfsd4_cstate_clear_replay(struct nfsd4_compound_state *cstate)
>  
>  	if (so != NULL) {
>  		cstate->replay_owner = NULL;
> -		atomic_set(&so->so_replay.rp_locked, RP_UNLOCKED);
> -		smp_mb__after_atomic();
> -		wake_up_var(&so->so_replay.rp_locked);
> +		store_release_wake_up(&so->so_replay.rp_locked, RP_UNLOCKED);
>  		nfs4_put_stateowner(so);
>  	}
>  }
> @@ -5069,9 +5067,7 @@ move_to_close_lru(struct nfs4_ol_stateid *s, struct net *net)
>  	 * Some threads with a reference might be waiting for rp_locked,
>  	 * so tell them to stop waiting.
>  	 */
> -	atomic_set(&oo->oo_owner.so_replay.rp_locked, RP_UNHASHED);
> -	smp_mb__after_atomic();
> -	wake_up_var(&oo->oo_owner.so_replay.rp_locked);
> +	store_release_wake_up(&oo->oo_owner.so_replay.rp_locked, RP_UNHASHED);
>  	wait_event(close_wq, refcount_read(&s->st_stid.sc_count) == 2);
>  
>  	release_all_access(s);
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index e16bb3717fb9..ba30b2335b66 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -505,7 +505,7 @@ struct nfs4_replay {
>  	unsigned int		rp_buflen;
>  	char			*rp_buf;
>  	struct knfsd_fh		rp_openfh;
> -	atomic_t		rp_locked;
> +	int			rp_locked;
>  	char			rp_ibuf[NFSD4_REPLAY_ISIZE];
>  };
>  

Looks good otherwise.

Reviewed-by: Jeff Layton <jlayton@kernel.org>