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

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Date: Fri, 17 Nov 2023 11:43:21 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Sascha Hauer <s.hauer@...gutronix.de>, Jens Axboe <axboe@...nel.dk>,
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, kernel@...gutronix.de
Subject: Re: [PATCH] net: Do not break out of sk_stream_wait_memory() with
 TIF_NOTIFY_SIGNAL

On 27.10.2023 14:04:32, Sascha Hauer wrote:
> On Thu, Oct 26, 2023 at 10:49:18AM +0200, Paolo Abeni wrote:
> > 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.
> 
> I don't think there's anything I can do in tls_sw_release_resources_tx().
> When entering this function TIF_NOTIFY_SIGNAL is not (yet) set. It gets
> set at some point while tls_sw_release_resources_tx() is running. I find
> it set when tls_tx_records() returns with -ERESTARTSYS. I tried clearing
> TIF_NOTIFY_SIGNAL then and called tls_tx_records() again, but that doesn't
> work.

Seems the discussion got stuck, what are the blocking points?

Marc

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