linux-kernel - Re: [PATCH]: use spin_lock_irqsave in try_one

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Date:	Tue, 3 Nov 2009 22:58:54 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH]: use spin_lock_irqsave in try_one_irq()

> This happens because the &desc->lock is taken with spin_lock_irqsave and
> just a spin_lock.  In the try_one_irq(), this lock really should be a
> spin_lock_irqsave().
>

Cc'ed Ingo and Thomas.

The reason is that try_one_irq() is called both from hardirq context and softirq
context. And by default the timer handler poll_all_shared_irqs() is
called with irq enabled.
Then the two usage will cause inconsistent.

So I think the following patch is also workable to you.

diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
index 114e704..11affbc 100644
--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -111,6 +111,7 @@ static void poll_all_shared_irqs(void)

 	for_each_irq_desc(i, desc) {
 		unsigned int status;
+		unsigned long flags;

 		if (!i)
 			 continue;
@@ -121,7 +122,9 @@ static void poll_all_shared_irqs(void)
 		if (!(status & IRQ_SPURIOUS_DISABLED))
 			continue;

+		local_irq_save(flags);
 		try_one_irq(i, desc);
+		local_irq_restore(flags);
 	}
 }

> I have not yet narrowed down the reason for the spurious interrupt (although
> I suspect it maybe to do with the radeon driver).
>
> Successfully tested by me.
>
> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
>
> --- linux-2.6.31.x86_64.orig/kernel/irq/spurious.c      2009-09-09 18:13:59.000000000 -0400
> +++ linux-2.6.31.x86_64/kernel/irq/spurious.c   2009-10-26 10:55:56.709845786 -0400
> @@ -27,8 +27,9 @@ static int try_one_irq(int irq, struct i
>  {
>        struct irqaction *action;
>        int ok = 0, work = 0;
> +       unsigned long flags;
>
> -       spin_lock(&desc->lock);
> +       spin_lock_irqsave(&desc->lock, flags);
>        /* Already running on another processor */
>        if (desc->status & IRQ_INPROGRESS) {
>                /*
> @@ -37,13 +38,13 @@ static int try_one_irq(int irq, struct i
>                 */
>                if (desc->action && (desc->action->flags & IRQF_SHARED))
>                        desc->status |= IRQ_PENDING;
> -               spin_unlock(&desc->lock);
> +               spin_unlock_irqrestore(&desc->lock, flags);
>                return ok;
>        }
>        /* Honour the normal IRQ locking */
>        desc->status |= IRQ_INPROGRESS;
>        action = desc->action;
> -       spin_unlock(&desc->lock);
> +       spin_unlock_irqrestore(&desc->lock, flags);
>
>        while (action) {
>                /* Only shared IRQ handlers are safe to call */
> @@ -56,7 +57,7 @@ static int try_one_irq(int irq, struct i
>        }
>        local_irq_disable();
>        /* Now clean up the flags */
> -       spin_lock(&desc->lock);
> +       spin_lock_irqsave(&desc->lock, flags);
>        action = desc->action;
>
>        /*
> @@ -68,9 +69,9 @@ static int try_one_irq(int irq, struct i
>                 * Perform real IRQ processing for the IRQ we deferred
>                 */
>                work = 1;
> -               spin_unlock(&desc->lock);
> +               spin_unlock_irqrestore(&desc->lock, flags);
>                handle_IRQ_event(irq, action);
> -               spin_lock(&desc->lock);
> +               spin_lock_irqsave(&desc->lock, flags);
>                desc->status &= ~IRQ_PENDING;
>        }
>        desc->status &= ~IRQ_INPROGRESS;
> @@ -80,7 +81,7 @@ static int try_one_irq(int irq, struct i
>         */
>        if (work && desc->chip && desc->chip->end)
>                desc->chip->end(irq);
> -       spin_unlock(&desc->lock);
> +       spin_unlock_irqrestore(&desc->lock, flags);
>
>        return ok;
>  }
> --
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