linux-kernel - Re: [PATCH 2/2] perf,hw_breakpoint: Initialize hardware api earlier

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Date:	Sat, 13 Nov 2010 22:46:06 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Jason Wessel <jason.wessel@...driver.com>
Subject: Re: [PATCH 2/2] perf,hw_breakpoint: Initialize hardware api earlier

On Sat, 2010-11-13 at 22:37 +0100, Frederic Weisbecker wrote:
> From: Jason Wessel <jason.wessel@...driver.com>
> 
> When using early debugging, the kernel does not initialize the
> hw_breakpoint API early enough and causes the late initialization of
> the kernel debugger to fail. The boot arguments are:
> 
>     earlyprintk=vga ekgdboc=kbd kgdbwait
> 
> Then simply type "go" at the kdb prompt and boot. The kernel will
> later emit the message:
> 
>     kgdb: Could not allocate hwbreakpoints
> 
> And at that point the kernel debugger will cease to work correctly.
> 
> The solution is to initialize the hw_breakpoint at the same time that
> all the other perf call backs are initialized instead of using a
> core_initcall() initialization which happens well after the kernel
> debugger can make use of hardware breakpoints.

How early is it needed? I've got a patch converting the x86 (still need
to do the other hardware pmus) to early_initcall() instead of random
places in the arch bringup (notably before the perf core init).


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