netdev - Re: [PATCH] net: Do not break out of sk_stream_wait_memory() with TIF_NOTIFY

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Date: Thu, 26 Oct 2023 10:49:18 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Sascha Hauer <s.hauer@...gutronix.de>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, "David S . Miller"
	 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Jens Axboe
	 <axboe@...nel.dk>, kernel@...gutronix.de
Subject: Re: [PATCH] net: Do not break out of sk_stream_wait_memory() with
 TIF_NOTIFY_SIGNAL

On Thu, 2023-10-26 at 09:03 +0200, Sascha Hauer wrote:
> On Tue, Oct 24, 2023 at 03:56:17PM +0200, Paolo Abeni wrote:
> > On Mon, 2023-10-23 at 14:13 +0200, Sascha Hauer wrote:
> > > It can happen that a socket sends the remaining data at close() time.
> > > With io_uring and KTLS it can happen that sk_stream_wait_memory() bails
> > > out with -512 (-ERESTARTSYS) because TIF_NOTIFY_SIGNAL is set for the
> > > current task. This flag has been set in io_req_normal_work_add() by
> > > calling task_work_add().
> > > 
> > > It seems signal_pending() is too broad, so this patch replaces it with
> > > task_sigpending(), thus ignoring the TIF_NOTIFY_SIGNAL flag.
> > 
> > This looks dangerous, at best. Other possible legit users setting
> > TIF_NOTIFY_SIGNAL will be broken.
> > 
> > Can't you instead clear TIF_NOTIFY_SIGNAL in io_run_task_work() ?
> 
> I don't have an idea how io_run_task_work() comes into play here, but it
> seems it already clears TIF_NOTIFY_SIGNAL:
> 
> static inline int io_run_task_work(void)
> {
>         /*
>          * Always check-and-clear the task_work notification signal. With how
>          * signaling works for task_work, we can find it set with nothing to
>          * run. We need to clear it for that case, like get_signal() does.
>          */
>         if (test_thread_flag(TIF_NOTIFY_SIGNAL))
>                 clear_notify_signal();
> 	...
> }

I see, io_run_task_work() is too late, sk_stream_wait_memory() is
already woken up.

I still think this patch is unsafe. What about explicitly handling the
restart in tls_sw_release_resources_tx() ? The main point is that such
function is called by inet_release() and the latter can't be re-
started.

Cheers,

Paolo