linux-kernel - Re: [PATCH 3/5] kernel: add support for TIF_NOTIFY

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Message-ID: <20201015143151.GB24156@redhat.com>
Date:   Thu, 15 Oct 2020 16:31:52 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-kernel@...r.kernel.org, io-uring@...r.kernel.org,
        peterz@...radead.org, tglx@...utronix.de
Subject: Re: [PATCH 3/5] kernel: add support for TIF_NOTIFY_SIGNAL

On 10/15, Jens Axboe wrote:
>
>  static inline int signal_pending(struct task_struct *p)
>  {
> +#if defined(CONFIG_GENERIC_ENTRY) && defined(TIF_NOTIFY_SIGNAL)
> +	/*
> +	 * TIF_NOTIFY_SIGNAL isn't really a signal, but it requires the same
> +	 * behavior in terms of ensuring that we break out of wait loops
> +	 * so that notify signal callbacks can be processed.
> +	 */
> +	if (unlikely(test_tsk_thread_flag(p, TIF_NOTIFY_SIGNAL)))
> +		return 1;
> +#endif
>  	return task_sigpending(p);
>  }

I don't understand why does this version requires CONFIG_GENERIC_ENTRY.

Afaics, it is very easy to change all the non-x86 arches to support
TIF_NOTIFY_SIGNAL, but it is not trivial to change them all to use
kernel/entry/common.c ?

Oleg.