linux-kernel - Re: [tip:x86/irq] x86: Always use irq stacks

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Date:	Fri, 23 Jul 2010 10:24:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Christoph Hellwig <hch@....de>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/irq] x86: Always use irq stacks

On Fri, 2010-07-23 at 10:15 -0400, Steven Rostedt wrote:
> On Wed, 2010-07-14 at 17:47 +0200, Christoph Hellwig wrote:

> In arch/x86/kernel/dumpstack_32.c:
> 
>                 context = (struct thread_info *)
>                         ((unsigned long)stack & (~(THREAD_SIZE - 1)));
>                 bp = ops->walk_stack(context, stack, bp, ops, data, NULL, &graph);
> 
> Note: here, context (which ends up being tinfo) is just a bitmasking of
> the current stack. If the stack is the irqstack, then what is passed to
> walk_stack() is not the actual thread info structure.
> 
> Note, if THREAD_SIZE is 8k and irqstacks are 4K then context is totally
> wrong here.

irqstacks are indeed 8k as well, but:

union irq_ctx {
        struct thread_info      tinfo;
        u32                     stack[THREAD_SIZE/sizeof(u32)];
} __attribute__((aligned(PAGE_SIZE)));


The stack is 8k, but it is aligned 4k. Which will have

   context = (struct thread_info *)
                  ((unsigned long)stack & (~(THREAD_SIZE - 1)));

not give the expected result.

So we should do:

} __attribute__((aligned(THREAD_SIZE)));

-- Steve


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