linux-hardening - Re: [PATCH 0/7] wchan: Fix wchan support

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Date:   Thu, 14 Oct 2021 13:02:34 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Peter Zijlstra <peterz@...radead.org>
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Subject: Re: [PATCH 0/7] wchan: Fix wchan support

On Fri, Oct 08, 2021 at 01:15:27PM +0200, Peter Zijlstra wrote:
> Hi,
> 
> This fixes up wchan which is various degrees of broken across the
> architectures.
> 
> Patch 4 fixes wchan for x86, which has been returning 0 for the past many
> releases.
> 
> Patch 5 fixes the fundamental race against scheduling.
> 
> Patch 6 deletes a lot and makes STACKTRACE unconditional
> 
> patch 7 fixes up a few STACKTRACE arch oddities
> 
> 0day says all builds are good, so it must be perfect :-) I'm planning on
> queueing up at least the first 5 patches, but I'm hoping the last two patches
> can be too.
> 
> Also available here:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/wchan

These patches introduce a regression on ARM. Whereas before, I have
/proc/*/wchan populated with non-zero values, with these patches they
_all_ contain "0":

root@...arfog21:~# cat /proc/*/wchan
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000root@...arfog21:~#

I'll try to investigate what is going on later today.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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