linux-kernel - Re: [PATCH] nfsd: destroy percpu stats counters after reply cache shutdown

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Date:   Mon, 23 May 2022 19:25:29 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Julian Schroeder 
        <jumaco@...-dsk-jumaco-1e-78723413.us-east-1.amazon.com>
CC:     Amir Goldstein <amir73il@...il.com>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "benh@...zon.com" <benh@...zon.com>,
        "alisaidi@...zon.com" <alisaidi@...zon.com>,
        "jumaco@...zon.com" <jumaco@...zon.com>
Subject: Re: [PATCH] nfsd: destroy percpu stats counters after reply cache
 shutdown



> On May 23, 2022, at 2:52 PM, Julian Schroeder <jumaco@...-dsk-jumaco-1e-78723413.us-east-1.amazon.com> wrote:
> 
> From: Julian Schroeder <jumaco@...zon.com>
> 
> Upon nfsd shutdown any pending DRC cache is freed. DRC cache use is
> tracked via a percpu counter. In the current code the percpu counter
> is destroyed before. If any pending cache is still present,
> percpu_counter_add is called with a percpu counter==NULL. This causes
> a kernel crash.
> The solution is to destroy the percpu counter after the cache is freed.
> 
> Fixes: e567b98ce9a4b (“nfsd: protect concurrent access to nfsd stats counters”)
> Signed-off-by: Julian Schroeder <jumaco@...zon.com>
> ---
> fs/nfsd/nfscache.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index 0b3f12aa37ff..7da88bdc0d6c 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -206,7 +206,6 @@ void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
> 	struct svc_cacherep	*rp;
> 	unsigned int i;
> 
> -	nfsd_reply_cache_stats_destroy(nn);
> 	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
> 
> 	for (i = 0; i < nn->drc_hashsize; i++) {
> @@ -217,6 +216,7 @@ void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
> 									rp, nn);
> 		}
> 	}
> +	nfsd_reply_cache_stats_destroy(nn);
> 
> 	kvfree(nn->drc_hashtbl);
> 	nn->drc_hashtbl = NULL;
> -- 
> 2.32.0
> 

Thank you, Julian. Patch applied to the NFSD for-5.19 topic branch.

--
Chuck Lever