linux-kernel - Re: [PATCH] xen/events: xen/events: fix RCU warning

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Date:	Tue, 6 Nov 2012 11:17:42 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Mojiong Qiu <qiumojiong@...il.com>
Cc:	linux-kernel@...r.kernel.org, Mojiong Qiu <mjqiu@...cent.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	xen-devel@...ts.xensource.com,
	virtualization@...ts.linux-foundation.org,
	"at least to 3.0.y" <stable@...nel.org>
Subject: Re: [PATCH] xen/events: xen/events: fix RCU warning

On Tue, Nov 06, 2012 at 04:08:15PM +0800, Mojiong Qiu wrote:
> exit_idle() should be called after irq_enter(), otherwise it throws:

That seems odd - wouldn't "smp_x86_platform_ipi"
also need the same treatment [edit: I was looking at 3.0 kernel code] ?

Ah, this is caused by

commit 98ad1cc14a5c4fd658f9d72c6ba5c86dfd3ce0d5
Author: Frederic Weisbecker <fweisbec@...il.com>
Date:   Fri Oct 7 18:22:09 2011 +0200

    x86: Call idle notifier after irq_enter()
    

and it missed the xen-case

which means that any kernel v3.3 and newer need this, but earlier do
not.

Thx. Will put in 3.7 tree.

> 
> [    2.513020] [ INFO: suspicious RCU usage. ]
> [    2.513076] 3.6.5 #1 Not tainted
> [    2.513128] -------------------------------
> [    2.513183] include/linux/rcupdate.h:725 rcu_read_lock() used illegally while idle!
> [    2.513271]
> [    2.513271] other info that might help us debug this:
> [    2.513271]
> [    2.513388]
> [    2.513388] RCU used illegally from idle CPU!
> [    2.513388] rcu_scheduler_active = 1, debug_locks = 1
> [    2.513511] RCU used illegally from extended quiescent state!
> [    2.513572] 1 lock held by swapper/0/0:
> [    2.513626]  #0:  (rcu_read_lock){......}, at: [<ffffffff810e9fe0>] __atomic_notifier_call_chain+0x0/0x140
> [    2.513815]
> [    2.513815] stack backtrace:
> [    2.513897] Pid: 0, comm: swapper/0 Not tainted 3.6.5 #1
> [    2.513954] Call Trace:
> [    2.514005]  <IRQ>  [<ffffffff811259a2>] lockdep_rcu_suspicious+0xe2/0x130
> [    2.514107]  [<ffffffff810ea10c>] __atomic_notifier_call_chain+0x12c/0x140
> [    2.514169]  [<ffffffff810e9fe0>] ? atomic_notifier_chain_unregister+0x90/0x90
> [    2.514258]  [<ffffffff811216cd>] ? trace_hardirqs_off+0xd/0x10
> [    2.514318]  [<ffffffff810ea136>] atomic_notifier_call_chain+0x16/0x20
> [    2.514381]  [<ffffffff810777c3>] exit_idle+0x43/0x50
> [    2.514441]  [<ffffffff81568865>] xen_evtchn_do_upcall+0x25/0x50
> [    2.514503]  [<ffffffff81aa690e>] xen_do_hypervisor_callback+0x1e/0x30
> [    2.514562]  <EOI>  [<ffffffff810013aa>] ? hypercall_page+0x3aa/0x1000
> [    2.514662]  [<ffffffff810013aa>] ? hypercall_page+0x3aa/0x1000
> [    2.514722]  [<ffffffff81061540>] ? xen_safe_halt+0x10/0x20
> [    2.514782]  [<ffffffff81075cfa>] ? default_idle+0xba/0x570
> [    2.514841]  [<ffffffff810778af>] ? cpu_idle+0xdf/0x140
> [    2.514900]  [<ffffffff81a4d881>] ? rest_init+0x135/0x144
> [    2.514960]  [<ffffffff81a4d74c>] ? csum_partial_copy_generic+0x16c/0x16c
> [    2.515022]  [<ffffffff82520c45>] ? start_kernel+0x3db/0x3e8
> [    2.515081]  [<ffffffff8252066a>] ? repair_env_string+0x5a/0x5a
> [    2.515141]  [<ffffffff82520356>] ? x86_64_start_reservations+0x131/0x135
> [    2.515202]  [<ffffffff82524aca>] ? xen_start_kernel+0x465/0x46
> 
> Signed-off-by: Mojiong Qiu <mjqiu@...cent.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Jeremy Fitzhardinge <jeremy@...p.org>
> Cc: xen-devel@...ts.xensource.com
> Cc: virtualization@...ts.linux-foundation.org
> Cc: linux-kernel@...r.kernel.org
> Cc: stable@...nel.org (at least to 3.0.y)
             ^^^- vger.kernel.org

You mean 3.3.x

> ---
>  drivers/xen/events.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index 912ac81..0be4df3 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -1395,10 +1395,10 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
>  {
>  	struct pt_regs *old_regs = set_irq_regs(regs);
>  
> +	irq_enter();
>  #ifdef CONFIG_X86
>  	exit_idle();
>  #endif
> -	irq_enter();
>  
>  	__xen_evtchn_do_upcall();
>  
> -- 
> 1.6.3.2
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