Re: [PATCH 0/7] wchan: Fix wchan support

Russell King (Oracle)
2021-10-14T12:03:28Z

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@clearfog21:~# cat /proc/*/wchan
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000root@clearfog21:~#

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

--
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