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 <redacted>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Anton Blanchard <redacted> 

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.