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

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Date:   Thu, 26 Oct 2023 09:03:10 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     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>, 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 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();
	...
}

Sascha

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