Re: 5.8-rc*: kernel BUG at kernel/signal.c:1917

[peterz@infradead.org]

On Tue, Jul 21, 2020 at 12:52:52AM -0400, Paul Gortmaker wrote:
> [Re: 5.8-rc*: kernel BUG at kernel/signal.c:1917] On 20/07/2020 (Mon 16:21) Peter Zijlstra wrote:
> 
> > On Mon, Jul 20, 2020 at 04:02:24PM +0200, Oleg Nesterov wrote:
> > > I have to admit, I do not understand the usage of prev_state in schedule(),
> > > it looks really, really subtle...
> > 
> > Right, so commit dbfb089d360 solved a problem where schedule() re-read
> > prev->state vs prev->on_rq = 0. That is, schedule()'s dequeue and
> > ttwu()'s enqueue disagreed over sched_contributes_to_load. and as a
> > result load-accounting went wobbly.
> > 
> > Now, looking at that commit again, I might've solved the problem twice
> > :-P
> 
> [...]
> 
> > That said, in a crossed email, I just proposed we could simplify all
> > this like so.. but now I need to go ask people to re-validate that
> > loadavg muck again :-/
> 
> After a two hour "quick" sanity test I then gave it a full 7h run (which
> always seemed to break before dbfb089d360) and I didn't see any stuck
> load average with master from today + this change.
> 
> Paul.
> 
> root@t5610:/home/paul/git/linux-head#
> [1]+  Done                    nohup tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 24 --duration 420 --configs TREE03 --trust-make > /tmp/kvm.sh.out 2>&1
> root@t5610:/home/paul/git/linux-head# cat /proc/version
> Linux version 5.8.0-rc6-00001-g5714ee50bb43-dirty (paul@t5610) (gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #3 SMP Mon Jul 20 12:30:33 EDT 2020
> root@t5610:/home/paul/git/linux-head# uptime
>  00:49:18 up  7:41,  2 users,  load average: 0.01, 0.00, 0.63
> root@t5610:/home/paul/git/linux-head# 
> 
> --

Thanks a lot for re-testing that Paul, much appreciated!

Let me go write a Changelog for this then...