linux-kernel - Re: [PATCH 18/41] OpenRISC: Don't reimplement force

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Date:	Tue, 16 Aug 2011 18:49:28 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	linux-kernel@...r.kernel.org, Jonas Bonn <jonas@...thpole.se>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 18/41] OpenRISC: Don't reimplement force_sigsegv()

On 08/11, Matt Fleming wrote:
>
> Instead of open coding the sequence from force_sigsegv() just call
> it. This also fixes a race because sa_handler was being modified
> without holding ->sighand->siglock.
>
> --- a/arch/openrisc/kernel/signal.c
> +++ b/arch/openrisc/kernel/signal.c
> @@ -257,9 +257,7 @@ static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
>  	return;
>
>  give_sigsegv:
> -	if (sig == SIGSEGV)
> -		ka->sa.sa_handler = SIG_DFL;
> -	force_sig(SIGSEGV, current);
> +	force_sigsegv(sig, current);
>  }

Agreed, but...

I don't really understand the changelog, which race this patch fix?

Yes, we shouldn't change sa_handler lockless, this "breaks the rules"
but I do not see any immediate problem. And since force_sigsegv() drops
the lock after setting SIG_DFL we can "race" with the sub-thread anyway.

Hmm. Looking more, I think that this patch is not the cleanup, but the
bugfix. The current code is simply wrong, it plays with ka, and it points
to the _copy_ of sighand->action[], so this code is simply pointless.

Unless I missed something, could you fix the changelog and resend?

Oleg.

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