[Top] [All Lists]

Re: [PATCH] MIPS: cavium: Don't enable irq in ->init__secondary()

To: Yong Zhang <>, Ralf Baechle <>
Subject: Re: [PATCH] MIPS: cavium: Don't enable irq in ->init__secondary()
From: David Daney <>
Date: Tue, 17 Apr 2012 13:45:50 -0700
Cc:, David Daney <>
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20120113; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; bh=Q5UFV3riz7fmfx9N5ped6x7GkKHiLrLesiFMF26ylJQ=; b=D7J8yy/xu0QtxU/aNbUU73Q7tHGipCJkbJaqTz3k8YTgjyygSMgqt+AbKtczNKo1Sb zkCGKRlVDleTH+kX7lnEhev7w6cM2vUZ2X+7RZjlYSkchwAKsjRocdoJM+NHKEabuqAz y7hpmVCeKTY2WgPidqlHbFcqZ8LkEJKuDpGRsmi2UNiimVYcFhop05BqbeZi6HWve3Nt yvQGCoJwZS37+ewK0bGz0sHzSWHOpCrXwC7IkdbSQwvYooH7drrqcjAfU+DDMVD7H7Tj O+uolIp41Q/rGkD+uit07QmtwTRYlu87AeZEWkhlFYJ0cnACpLOads3I6+U4ppxJStJC IcCw==
In-reply-to: <20120417030848.GA6377@zhy>
References: <> <> <20120417030848.GA6377@zhy>
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10
On 04/16/2012 08:08 PM, Yong Zhang wrote:
On Mon, Apr 16, 2012 at 09:48:14AM -0700, David Daney wrote:
On 04/16/2012 12:25 AM, Yong Zhang wrote:
From: Yong Zhang<>

Too early to enable irq will break some following action,
such as notify_cpu_starting().

Can you be more specific about what breaks?

For example:

        CPU1                            CPU2
                                do something;
                                      wake up softirqd;
                                        /* select wrong cpu */

Yeah, that looks broken to me too.

I don't get side effect with this patch.

Without this, where do irqs get enabled on the secondary CPUs?

cpu_idle() will handle it. But in fact we should not depend on

It is not done in cpu_idle() itself. If irqs are disabled upon entry to cpu_idle() *and* need_resched(), then we call into schedule(). The irqs are then enabled by the raw_spin_unlock_irq(&rq->lock) at the end of kernel/sched/core.c: __schedule().

But it seems there is not suitable place to put local_irq_enable(),
though ->smp_finish() looks like a more suitable place.

It would be better, but it seems like really it should be done in cpu_idle() immediately after rcu_idle_enter().

When looking more at smp support on MIPS, there is more things I find.
Such as set_cpu_online() is called on CPU1, so there will be another race
window like above scenario. Please take a look at what commit 2baab4e9
intend to resolve.


Signed-off-by: Yong Zhang<>
Cc: David Daney<>
Cc: Ralf Baechle<>
  arch/mips/cavium-octeon/smp.c |    1 -
  1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/arch/mips/cavium-octeon/smp.c b/arch/mips/cavium-octeon/smp.c
index 97e7ce9..7e65c88 100644
--- a/arch/mips/cavium-octeon/smp.c
+++ b/arch/mips/cavium-octeon/smp.c
@@ -185,7 +185,6 @@ static void __cpuinit octeon_init_secondary(void)

-       raw_local_irq_enable();


<Prev in Thread] Current Thread [Next in Thread>