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

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Message-ID: <87cyv2wj4e.fsf@pengutronix.de>
Date: Tue, 19 Dec 2023 12:00:44 +0100
From: Steffen Trumtrar <s.trumtrar@...gutronix.de>
To: Marc Kleine-Budde <mkl@...gutronix.de>
Cc: Sascha Hauer <s.hauer@...gutronix.de>, Jens Axboe <axboe@...nel.dk>,
 Paolo Abeni <pabeni@...hat.com>, 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 2023-11-17 at 11:43 +01, Marc Kleine-Budde <mkl@...gutronix.de> wrote:

> [[PGP Signed Part:Undecided]]
> 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?

Ping!

Any pointers on how to get this sorted out?


Best regards,
Steffen

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