linux-kernel - Re: [patch 01/20] idle: Move x86ism out of generic code

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Message-ID: <alpine.DEB.2.11.1602292026050.3638@nanos>
Date:	Mon, 29 Feb 2016 20:35:41 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Brian Gerst <brgerst@...il.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Peter Anvin <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	linux-arch@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	"Srivatsa S. Bhat" <srivatsa@....edu>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	Paul Turner <pjt@...gle.com>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [patch 01/20] idle: Move x86ism out of generic code

On Sat, 27 Feb 2016, Brian Gerst wrote:
> >         arch_cpu_idle_prepare();
> >         cpu_idle_loop();
> >  }
> 
> Does this actually work with stack protector enabled?
> boot_init_stack_canary() is inlined while arch_cpu_idle_prepare() is
> not.

Stupid me. No it does of course not. I could have sworn that I tested that,
but obvioulsy not.

I drop that patch, but actually the real question is whether we can drop that
'#ifdef x86' around that boot_init_stack_canary() invocation.

AFAICT, neither arm, arm64 nor mips and sh call it on anything else than the
boot cpu. I can't see why that would be an issue on those architectures and
why it would be a problem if the boot cpu calls it again here.

CC'ed the relevant maintainers. Is there any issue with the patch below?

Thanks,

	tglx

8<------------------

--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -276,12 +276,6 @@ static void cpu_idle_loop(void)
 void cpu_startup_entry(enum cpuhp_state state)
 {
 	/*
-	 * This #ifdef needs to die, but it's too late in the cycle to
-	 * make this generic (arm and sh have never invoked the canary
-	 * init for the non boot cpus!). Will be fixed in 3.11
-	 */
-#ifdef CONFIG_X86
-	/*
 	 * If we're the non-boot CPU, nothing set the stack canary up
 	 * for us. The boot CPU already has it initialized but no harm
 	 * in doing it again. This is a good place for updating it, as
@@ -289,7 +283,7 @@ void cpu_startup_entry(enum cpuhp_state
 	 * canaries already on the stack wont ever trigger).
 	 */
 	boot_init_stack_canary();
-#endif
+
 	arch_cpu_idle_prepare();
 	cpu_idle_loop();
 }