linux-kernel - Re: [PATCH] perf: powerpc: Disable pagefaults during callchain stack read

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Date:	Mon, 01 Aug 2011 11:59:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Ahern <dsahern@...il.com>
Cc:	benh@...nel.crashing.org, anton@...ba.org, acme@...stprotocols.net,
	mingo@...e.hu, paulus@...ba.org, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: powerpc: Disable pagefaults during callchain
 stack read

On Sat, 2011-07-30 at 14:53 -0600, David Ahern wrote:
> A page fault occurred walking the callchain while creating a perf
> sample for the context-switch event. To handle the page fault the
> mmap_sem is needed, but it is currently held by setup_arg_pages.
> (setup_arg_pages calls shift_arg_pages with the mmap_sem held.
> shift_arg_pages then calls move_page_tables which has a cond_resched
> at the top of its for loop - hitting that cond_resched is what caused
> the context switch.)
> 
> This is an extension of Anton's proposed patch:
> https://lkml.org/lkml/2011/7/24/151
> adding case for 32-bit ppc.
> 
> Tested on the system that first generated the panic and then again
> with latest kernel using a PPC VM. I am not able to test the 64-bit
> path - I do not have H/W for it and 64-bit PPC VMs (qemu on Intel)
> is horribly slow.
> 
> Signed-off-by: David Ahern <dsahern@...il.com>
> CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> CC: Anton Blanchard <anton@...ba.org> 

Hmm, Paul, didn't you fix something like this early on? Anyway, I've no
objections since I'm really not familiar enough with the PPC side of
things.

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