linux-kernel - Re: [PATCH] nfsd: fix oops when reading pool

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Date: Mon, 17 Jun 2024 19:23:45 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: Jeff Layton <jlayton@...nel.org>, Chuck Lever <chuck.lever@...cle.com>,
        Neil Brown <neilb@...e.de>, Olga Kornievskaia <kolga@...app.com>,
        Dai Ngo <Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>
Cc: Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nfsd: fix oops when reading pool_stats before server is
 started

Hello Jeff,

With the below fix applied, the issue is not observed.
Tested-by: Sourabh Jain <sourabhjain@...ux.ibm.com>

Thanks for the fix.

- Sourabh Jain

On 17/06/24 17:24, Jeff Layton wrote:
> Sourbh reported an oops that is triggerable by trying to read the
> pool_stats procfile before nfsd had been started. Move the check for a
> NULL serv in svc_pool_stats_start above the mutex acquisition, and fix
> the stop routine not to unlock the mutex if there is no serv yet.
>
> Fixes: 7b207ccd9833 ("svc: don't hold reference for poolstats, only mutex.")
> Reported-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>   net/sunrpc/svc_xprt.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index d3735ab3e6d1..b757a8891813 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -1422,12 +1422,13 @@ static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
>   
>   	dprintk("svc_pool_stats_start, *pidx=%u\n", pidx);
>   
> +	if (!si->serv)
> +		return NULL;
> +
>   	mutex_lock(si->mutex);
>   
>   	if (!pidx)
>   		return SEQ_START_TOKEN;
> -	if (!si->serv)
> -		return NULL;
>   	return pidx > si->serv->sv_nrpools ? NULL
>   		: &si->serv->sv_pools[pidx - 1];
>   }
> @@ -1459,7 +1460,8 @@ static void svc_pool_stats_stop(struct seq_file *m, void *p)
>   {
>   	struct svc_info *si = m->private;
>   
> -	mutex_unlock(si->mutex);
> +	if (si->serv)
> +		mutex_unlock(si->mutex);
>   }
>   
>   static int svc_pool_stats_show(struct seq_file *m, void *p)
>
> ---
> base-commit: 4ddfda417a50309f17aeb85f8d1a9a9efbc7d81c
> change-id: 20240617-nfsd-next-8593f73544f5
>
> Best regards,