linux-kernel - Re: [RFC PATCH v2 1/3] restartable sequences: user-space per-cpu critical sections

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Message-ID: <1447951090.2765.9.camel@sipsolutions.net>
Date:	Thu, 19 Nov 2015 17:38:10 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Paul Turner <commonly@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Hunter <ahh@...gle.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andi Kleen <andi@...stfloor.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Dave Watson <davejwatson@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
	Josh Triplett <josh@...htriplett.org>,
	Ingo Molnar <mingo@...hat.com>, Chris Lameter <cl@...ux.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH v2 1/3] restartable sequences: user-space per-cpu
 critical sections

On Tue, 2015-10-27 at 16:56 -0700, Paul Turner wrote:
> 
> + *  flags is currently unused.
> + */
> +SYSCALL_DEFINE3(restartable_sequences,
> +> 	> 	> int, flags, long, event_and_cpu, long, post_commit_instr_addr)
	
> +{
> +	return rseq_configure_current((__user u64 *)event_and_cpu,
> +				      (__user void *)post_commit_instr_addr);

It seems that, for forward compatibility and actually usefulness of the
'flags' argument, you need to reject the syscall if it's passed non-
zero right now. Otherwise applications can (inadvertedly) pass garbage
and you'll not be able to use it in the future.

johannes
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