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Date:   Thu, 23 Feb 2017 13:24:34 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Andi Kleen <andi@...stfloor.org>,
        Jan Stancek <jstancek@...hat.com>
Subject: Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage!

On Mon, Nov 21, 2016 at 10:28:50AM +0100, Peter Zijlstra wrote:
> On Mon, Nov 21, 2016 at 01:53:43AM +0100, Jiri Olsa wrote:
> > hi,
> > Jan hit following output when msr tracepoints are enabled on amd server:
> > 
> > [   91.585653] ===============================
> > [   91.589840] [ INFO: suspicious RCU usage. ]
> > [   91.594025] 4.9.0-rc1+ #1 Not tainted
> > [   91.597691] -------------------------------
> > [   91.601877] ./arch/x86/include/asm/msr-trace.h:42 suspicious rcu_dereference_check() usage!
> > [   91.610222] 
> > [   91.610222] other info that might help us debug this:
> > [   91.610222] 
> > [   91.618224] 
> > [   91.618224] RCU used illegally from idle CPU!
> > [   91.618224] rcu_scheduler_active = 1, debug_locks = 0
> > [   91.629081] RCU used illegally from extended quiescent state!
> > [   91.634820] no locks held by swapper/1/0.
> > [   91.638832] 
> > [   91.638832] stack backtrace:
> > [   91.643192] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0-rc1+ #1
> > [   91.649457] Hardware name: empty empty/S3992, BIOS 'V2.03   ' 05/09/2008
> > [   91.656159]  ffffc900018fbdf8 ffffffff813ed43c ffff88017ede8000 0000000000000001
> > [   91.663637]  ffffc900018fbe28 ffffffff810fdcd7 ffff880233f95dd0 00000000c0010055
> > [   91.671107]  0000000000000000 0000000000000000 ffffc900018fbe58 ffffffff814297ac
> > [   91.678560] Call Trace:
> > [   91.681022]  [<ffffffff813ed43c>] dump_stack+0x85/0xc9
> > [   91.686164]  [<ffffffff810fdcd7>] lockdep_rcu_suspicious+0xe7/0x120
> > [   91.692429]  [<ffffffff814297ac>] do_trace_read_msr+0x14c/0x1b0
> > [   91.698349]  [<ffffffff8106ddb2>] native_read_msr+0x32/0x40
> > [   91.703921]  [<ffffffff8103b2be>] amd_e400_idle+0x7e/0x110
> > [   91.709407]  [<ffffffff8103b78f>] arch_cpu_idle+0xf/0x20
> > [   91.714720]  [<ffffffff8181cd33>] default_idle_call+0x23/0x40
> > [   91.720467]  [<ffffffff810f306a>] cpu_startup_entry+0x1da/0x2b0
> > [   91.726387]  [<ffffffff81058b1f>] start_secondary+0x17f/0x1f0
> > 
> > 
> > it got away with attached change.. but this rcu logic
> > is far beyond me, so it's just wild guess.. ;-)
> 
> I think I prefer something like the below, that only annotates the one
> RDMSR in question, instead of all of them.
> 
> 
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 0888a879120f..d6c6aa80675f 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -357,7 +357,7 @@ static void amd_e400_idle(void)
>  	if (!amd_e400_c1e_detected) {
>  		u32 lo, hi;
>  
> -		rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi);
> +		RCU_NONIDLE(rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi));
>  
>  		if (lo & K8_INTP_C1E_ACTIVE_MASK) {
>  			amd_e400_c1e_detected = true;

hum, I might have missed some other solution in discussion,
and can't see this one being pulled in.. should I resend this?

thanks,
jirka

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