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From:   "Benjamin Coddington" <bcodding@redhat.com>
To:     "Trond Myklebust" <trondmy@hammerspace.com>
Cc:     Anna.Schumaker@netapp.com, linux-nfs@vger.kernel.org,
        jamespharvey20@gmail.com
Subject: Re: [PATCH] SUNRPC: fix race to sk_err after xs_error_report
Date:   Wed, 02 Oct 2019 06:41:44 -0400
Message-ID: <605DFB04-3686-4CCE-A87E-905E91E01F50@redhat.com>
In-Reply-To: <d9bf3f1092ed0361cc344e04a915ea337a3aa9e8.camel@hammerspace.com>
References: <9796ba15d926f65923965c2aedf777aaa59861e8.1569954618.git.bcodding@redhat.com>
 <d9bf3f1092ed0361cc344e04a915ea337a3aa9e8.camel@hammerspace.com>
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On 1 Oct 2019, at 15:38, Trond Myklebust wrote:

> On Tue, 2019-10-01 at 14:30 -0400, Benjamin Coddington wrote:
>> ...
>> diff --git a/include/linux/sunrpc/xprtsock.h
>> b/include/linux/sunrpc/xprtsock.h
>> index 7638dbe7bc50..8ffae73dea6c 100644
>> --- a/include/linux/sunrpc/xprtsock.h
>> +++ b/include/linux/sunrpc/xprtsock.h
>> @@ -56,6 +56,7 @@ struct sock_xprt {
>>  	 */
>>  	unsigned long		sock_state;
>>  	struct delayed_work	connect_worker;
>> +	int			xprt_err;
>
> Perhaps move this down just after srcport so we don't create an
> unnecessary hole in the structure?

Ok!

>>  	struct work_struct	error_worker;
>>  	struct work_struct	recv_worker;
>>  	struct mutex		recv_mutex;
>> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
>> index e2176c167a57..7fe77eef7080 100644
>> --- a/net/sunrpc/xprtsock.c
>> +++ b/net/sunrpc/xprtsock.c
>> @@ -1250,12 +1250,12 @@ static void xs_error_report(struct sock *sk)
>>  		goto out;
>>
>>  	transport = container_of(xprt, struct sock_xprt, xprt);
>> -	err = -sk->sk_err;
>> -	if (err == 0)
>> +	transport->xprt_err = -sk->sk_err;
>
> Doesn't this need a smp write barrier to ensure it isn't reordered with
> the set_bit() in xs_run_error_worker()?

Yes, it does need that or the error_worker may clear the bit without seeing
the error.

Ben