linux-kernel - Re: [PATCH -rt] MIPS: Octeon: convert smp_reserve

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Date:	Thu, 17 May 2012 22:50:03 +0200
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	Yong Zhang <yong.zhang0@...il.com>, linux-rt-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, david.daney@...ium.com,
	tglx@...utronix.de
Subject: Re: [PATCH -rt] MIPS: Octeon: convert smp_reserve_lock to raw
 spinlock

On Thu, May 17, 2012 at 09:30:42AM -0700, David Daney wrote:
> Date:   Thu, 17 May 2012 09:30:42 -0700
> From: David Daney <ddaney.cavm@...il.com>
> To: Yong Zhang <yong.zhang0@...il.com>, ralf@...ux-mips.org
> CC: linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
>  david.daney@...ium.com, tglx@...utronix.de
> Subject: Re: [PATCH -rt] MIPS: Octeon: convert smp_reserve_lock to raw
>  spinlock
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> On 05/17/2012 03:15 AM, Yong Zhang wrote:
> >From: Yong Zhang<yong.zhang@...driver.com>
> >
> >Because __cpu_disable is called in atomic context and spinlock
> >is a mutex on -rt.
> >
> >Signed-off-by: Yong Zhang<yong.zhang0@...il.com>
> >---
> >  arch/mips/cavium-octeon/smp.c |    6 +++---
> >  1 files changed, 3 insertions(+), 3 deletions(-)
> >
> >diff --git a/arch/mips/cavium-octeon/smp.c b/arch/mips/cavium-octeon/smp.c
> >index ef9c34a..473c72b 100644
> >--- a/arch/mips/cavium-octeon/smp.c
> >+++ b/arch/mips/cavium-octeon/smp.c
> >@@ -257,7 +257,7 @@ DEFINE_PER_CPU(int, cpu_state);
> >
> >  extern void fixup_irqs(void);
> >
> >-static DEFINE_SPINLOCK(smp_reserve_lock);
> >+static DEFINE_RAW_SPINLOCK(smp_reserve_lock);
> >
> 
> Ralf added this in 773cb77d (MIPS: Cavium: Add CPU hotplugging code.)
> 
> I'm not even sure what this lock is supposed to be protecting, so I
> would like Ralf to take a look.
> 
> You can add an Acked-by: from me for either this patch as is, or if
> Ralf thinks it is OK, removing the lock entirely.
> 
> In any event we can merge this via Ralf's tree.

The 773cb77d patch has a long history but I think I first worked on it for
Wind River Linux 2.0 which was 2.6.21-based, then broke it out and pushed
it upstream.  In 2.6.21 it was probably infected by the the smp_reserve_lock
virus in the s390 code for no good reason.  So I agree, the lock can
be dropped and I'm queueing a patch to do so for 3.5.

  Ralf
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