linux-kernel - Re: [PATCH 4/7] um: time-travel/signals: fix ndelay() in interrupt

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Date:   Thu, 25 Feb 2021 14:13:33 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     linux-um@...ts.infradead.org
Cc:     Arnd Bergmann <arnd@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] um: time-travel/signals: fix ndelay() in interrupt

On Tue, 2021-02-23 at 16:27 +0100, Johannes Berg wrote:
> 
> +void unblock_signals_hard(void)
> +{
> +	if (!signals_blocked)
> +		return;
> +
> +	if (signals_pending && signals_enabled) {
> +		/* this is a bit inefficient, but that's not really important */
> +		block_signals();
> +		unblock_signals();
> +	} else if (signals_pending & SIGIO_MASK) {
> +		/* we need to run time-travel handlers even if not enabled */
> +		sigio_run_timetravel_handlers();
> +	}
> +
> +	signals_blocked = 0;
> +}

This is, of course, racy & wrong - we could set signals_pending just
after checking it.

Need to make this

{
	if (!signals_blocked)
		return;
	signals_blocked = 0;
	barrier();

	if (signals_pending && signals_enabled) {
...


Anyway, I need to repost this series, but I'll wait a bit longer for
further feedback before that, since I know Arnd and others wanted to
take a look at the IOMEM and PCI bits.

johannes