netdev - Re: [PATCH 4/4] net/tls: implement ->read

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Message-ID: <476d2cd9-ae32-a4e6-4549-52c3863d4049@grimberg.me>
Date: Wed, 21 Jun 2023 12:49:21 +0300
From: Sagi Grimberg <sagi@...mberg.me>
To: Hannes Reinecke <hare@...e.de>, Jakub Kicinski <kuba@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Keith Busch <kbusch@...nel.org>,
 linux-nvme@...ts.infradead.org, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 Boris Pismenny <boris.pismenny@...il.com>
Subject: Re: [PATCH 4/4] net/tls: implement ->read_sock()



On 6/21/23 12:08, Hannes Reinecke wrote:
> On 6/21/23 10:39, Sagi Grimberg wrote:
>>
>>>> On Tue, 20 Jun 2023 16:21:22 +0300 Sagi Grimberg wrote:
>>>>>> +    err = tls_rx_reader_lock(sk, ctx, true);
>>>>>> +    if (err < 0)
>>>>>> +        return err;
>>>>>
>>>>> Unlike recvmsg or splice_read, the caller of read_sock is assumed to
>>>>> have the socket locked, and tls_rx_reader_lock also calls lock_sock,
>>>>> how is this not a deadlock?
>>>>
>>>> Yeah :|
>>>>
>>>>> I'm not exactly clear why the lock is needed here or what is the 
>>>>> subtle
>>>>> distinction between tls_rx_reader_lock and what lock_sock provides.
>>>>
>>>> It's a bit of a workaround for the consistency of the data stream.
>>>> There's bunch of state in the TLS ULP and waiting for mem or data
>>>> releases and re-takes the socket lock. So to stop the flow annoying
>>>> corner case races I slapped a lock around all of the reader.
>>>>
>>>> IMHO depending on the socket lock for anything non-trivial and outside
>>>> of the socket itself is a bad idea in general.
>>>>
>>>> The immediate need at the time was that if you did a read() and someone
>>>> else did a peek() at the same time from a stream of A B C D you may 
>>>> read
>>>> A D B C.
>>>
>>> Leaving me ever so confused.
>>>
>>> read_sock() is a generic interface; we cannot require a protocol 
>>> specific lock before calling it.
>>>
>>> What to do now?
>>> Drop the tls_rx_read_lock from read_sock() again?
>>
>> Probably just need to synchronize the readers by splitting that from
>> tls_rx_reader_lock:
>> -- 
>> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
>> index 53f944e6d8ef..53404c3fdcc6 100644
>> --- a/net/tls/tls_sw.c
>> +++ b/net/tls/tls_sw.c
>> @@ -1845,13 +1845,10 @@ tls_read_flush_backlog(struct sock *sk, struct 
>> tls_prot_info *prot,
>>          return sk_flush_backlog(sk);
>>   }
>>
>> -static int tls_rx_reader_lock(struct sock *sk, struct 
>> tls_sw_context_rx *ctx,
>> -                             bool nonblock)
>> +static int tls_rx_reader_acquire(struct sock *sk, struct 
>> tls_sw_context_rx *ctx,
>> +                            bool nonblock)
>>   {
>>          long timeo;
>> -       int err;
>> -
>> -       lock_sock(sk);
>>
>>          timeo = sock_rcvtimeo(sk, nonblock);
>>
>> @@ -1865,26 +1862,30 @@ static int tls_rx_reader_lock(struct sock *sk, 
>> struct tls_sw_context_rx *ctx,
>>                                !READ_ONCE(ctx->reader_present), &wait);
>>                  remove_wait_queue(&ctx->wq, &wait);
>>
>> -               if (timeo <= 0) {
>> -                       err = -EAGAIN;
>> -                       goto err_unlock;
>> -               }
>> -               if (signal_pending(current)) {
>> -                       err = sock_intr_errno(timeo);
>> -                       goto err_unlock;
>> -               }
>> +               if (timeo <= 0)
>> +                       return -EAGAIN;
>> +               if (signal_pending(current))
>> +                       return sock_intr_errno(timeo);
>>          }
>>
>>          WRITE_ONCE(ctx->reader_present, 1);
>>
>>          return 0;
>> +}
>>
>> -err_unlock:
>> -       release_sock(sk);
>> +static int tls_rx_reader_lock(struct sock *sk, struct 
>> tls_sw_context_rx *ctx,
>> +                             bool nonblock)
>> +{
>> +       int err;
>> +
>> +       lock_sock(sk);
>> +       err = tls_rx_reader_acquire(sk, ctx, nonblock);
>> +       if (err)
>> +               release_sock(sk);
>>          return err;
>>   }
>>
>> -static void tls_rx_reader_unlock(struct sock *sk, struct 
>> tls_sw_context_rx *ctx)
>> +static void tls_rx_reader_release(struct sock *sk, struct 
>> tls_sw_context_rx *ctx)
>>   {
>>          if (unlikely(ctx->reader_contended)) {
>>                  if (wq_has_sleeper(&ctx->wq))
>> @@ -1896,6 +1897,11 @@ static void tls_rx_reader_unlock(struct sock 
>> *sk, struct tls_sw_context_rx *ctx)
>>          }
>>
>>          WRITE_ONCE(ctx->reader_present, 0);
>> +}
>> +
>> +static void tls_rx_reader_unlock(struct sock *sk, struct 
>> tls_sw_context_rx *ctx)
>> +{
>> +       tls_rx_reader_release(sk, ctx);
>>          release_sock(sk);
>>   }
>> -- 
>>
>> Then read_sock can just acquire/release.
> 
> Good suggestion.
> Will be including it in the next round.

Maybe more appropriate helper names would be
tls_rx_reader_enter / tls_rx_reader_exit.

Whatever Jakub prefers...