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Message-ID: <8404022493c5ceda74807a3407e5a087425678e2.camel@redhat.com>
Subject: Re: [PATCH] net: Do not break out of sk_stream_wait_memory() with
 TIF_NOTIFY_SIGNAL
From:   Paolo Abeni <pabeni@redhat.com>
To:     Sascha Hauer <s.hauer@pengutronix.de>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        kernel@pengutronix.de
Date:   Thu, 26 Oct 2023 10:49:18 +0200
In-Reply-To: <20231026070310.GY3359458@pengutronix.de>
References: <20231023121346.4098160-1-s.hauer@pengutronix.de>
         <addf492843338e853f7fda683ce35050f26c9da0.camel@redhat.com>
         <20231026070310.GY3359458@pengutronix.de>
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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() bai=
ls
> > > 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().
> > >=20
> > > It seems signal_pending() is too broad, so this patch replaces it wit=
h
> > > task_sigpending(), thus ignoring the TIF_NOTIFY_SIGNAL flag.
> >=20
> > This looks dangerous, at best. Other possible legit users setting
> > TIF_NOTIFY_SIGNAL will be broken.
> >=20
> > Can't you instead clear TIF_NOTIFY_SIGNAL in io_run_task_work() ?
>=20
> I don't have an idea how io_run_task_work() comes into play here, but it
> seems it already clears TIF_NOTIFY_SIGNAL:
>=20
> 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