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Re: [PATCH] arch/mips: remove duplicate structure field initialization

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH] arch/mips: remove duplicate structure field initialization
From: "Kevin D. Kissell" <kevink@paralogos.com>
Date: Mon, 21 Sep 2009 13:23:45 -0700
Cc: Julia Lawall <julia@diku.dk>, dmitri.vorobiev@gmail.com, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org
In-reply-to: <20090921192520.GB17310@linux-mips.org>
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References: <Pine.LNX.4.64.0909211708200.8549@pc-004.diku.dk> <20090921192520.GB17310@linux-mips.org>
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I'm still on the mailing list, and had seen this going by. I'm not sure where that second .flags declaration got added. Way, way back when I was pretty much the only maintainer of the file, irq_ipi.flags was explicitly initialized to IRQF_DISABLED by an actual assignment statement in setp_cross_vpe_interrupts(), and the per-CPUness was handled by an "irq_desc[cpu_ipi_irq].status |= IRQ_PER_CPU". My guess is that first someone (maybe me) migrated the IRQF_DISABLED assignment into the declaration of the struct, and that later someone found the IRQ_PER_CPU thing bogus or deprecated and converted it into a second .flags line in the struct declaration, missing the fact that there was already one there.

In any case, I'm willing to sign off on Julia's patch. It's certainly more important that the IRQ be PER_CPU than initially DISABLED, but during the time when SMTC was seeing its heaviest testing at MIPS, both attributes were true.

         Regards,

         Kevin K.

Ralf Baechle wrote:
On Mon, Sep 21, 2009 at 05:08:55PM +0200, Julia Lawall wrote:

Adding Kevin "SMTC Kissel to cc.

From: Julia Lawall <julia@diku.dk>

The definition of the irq_ipi structure has two initializations of the
flags field.  This combines them.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@r@
identifier I, s, fld;
position p0,p;
expression E;
@@

struct I s =@p0 { ... .fld@p = E, ...};

@s@
identifier I, s, r.fld;
position r.p0,p;
expression E;
@@

struct I s =@p0 { ... .fld@p = E, ...};

@script:python@
p0 << r.p0;
fld << r.fld;
ps << s.p;
pr << r.p;
@@

if int(ps[0].line)!=int(pr[0].line) or int(ps[0].column)!=int(pr[0].column):
  cocci.print_main(fld,p0)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>

---
 arch/mips/kernel/smtc.c             |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/smtc.c b/arch/mips/kernel/smtc.c
index 67153a0..4d181df 100644
--- a/arch/mips/kernel/smtc.c
+++ b/arch/mips/kernel/smtc.c
@@ -1098,9 +1098,8 @@ static void ipi_irq_dispatch(void)
static struct irqaction irq_ipi = {
        .handler        = ipi_interrupt,
-       .flags          = IRQF_DISABLED,
-       .name           = "SMTC_IPI",
-       .flags          = IRQF_PERCPU
+       .flags          = IRQF_DISABLED | IRQF_PERCPU,
+       .name           = "SMTC_IPI"
 };
static void setup_cross_vpe_interrupts(unsigned int nvpe)

The actual semantic of this code as implemented by gcc is that all but the
last initializer are ignored so until somebody actually tests your code
I'll just remove the first of the two initializers and put a comment there.

  Ralf


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