netdev - Re: [PATCHv6 0/5] net/tls: fixes for NVMe-over-TLS

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Date: Mon, 3 Jul 2023 17:10:02 +0300
From: Sagi Grimberg <sagi@...mberg.me>
To: Hannes Reinecke <hare@...e.de>, David Howells <dhowells@...hat.com>
Cc: Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
 linux-nvme@...ts.infradead.org, Jakub Kicinski <kuba@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org
Subject: Re: [PATCHv6 0/5] net/tls: fixes for NVMe-over-TLS



On 7/3/23 16:57, Hannes Reinecke wrote:
> On 7/3/23 15:42, Sagi Grimberg wrote:
>>
>>>>> Hannes Reinecke <hare@...e.de> wrote:
>>>>>
>>>>>>> 'discover' and 'connect' works, but when I'm trying to transfer data
>>>>>>> (eg by doing a 'mkfs.xfs') the whole thing crashes horribly in
>>>>>>> sock_sendmsg() as it's trying to access invalid pages :-(
>>>>>
>>>>> Can you be more specific about the crash?
>>>>
>>>> Hannes,
>>>>
>>>> See:
>>>> [PATCH net] nvme-tcp: Fix comma-related oops
>>>
>>> Ah, right. That solves _that_ issue.
>>>
>>> But now I'm deadlocking on the tls_rx_reader_lock() (patched as to 
>>> your suggestion). Investigating.
>>
>> Are you sure it is a deadlock? or maybe you returned EAGAIN and nvme-tcp
>> does not interpret this as a transient status and simply returns from
>> io_work?
>>
> Unfortunately, yes.
> 
> static int tls_rx_reader_acquire(struct sock *sk, struct 
> tls_sw_context_rx *ctx,
>                                   bool nonblock)
> {
>          long timeo;
> 
>          timeo = sock_rcvtimeo(sk, nonblock);
> 
>          while (unlikely(ctx->reader_present)) {
>                  DEFINE_WAIT_FUNC(wait, woken_wake_function);
> 
>                  ctx->reader_contended = 1;
> 
>                  add_wait_queue(&ctx->wq, &wait);
>                  sk_wait_event(sk, &timeo,
>                                !READ_ONCE(ctx->reader_present), &wait);
> 
> and sk_wait_event() does:
> #define sk_wait_event(__sk, __timeo, __condition, __wait)              \
>          ({      int __rc;                                              \
>                  __sk->sk_wait_pending++;                               \
>                  release_sock(__sk);                                    \
>                  __rc = __condition;                                    \
>                  if (!__rc) {                                           \
>                          *(__timeo) = wait_woken(__wait,                \
>                                                  TASK_INTERRUPTIBLE,    \
>                                                  *(__timeo));           \
>                  }                                                      \
>                  sched_annotate_sleep();                                \
>                  lock_sock(__sk);                                       \
>                  __sk->sk_wait_pending--;                               \
>                  __rc = __condition;                                    \
>                  __rc;                                                  \
>          })
> 
> so not calling 'lock_sock()' in tls_tx_reader_acquire() helps only _so_ 
> much, we're still deadlocking.

That still is legal assuming that sock lock is taken prior to
sk_wait_event...

What are the blocked threads from sysrq-trigger?