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Subject: Re: Crash in fair scheduler
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>,
        "Schmid, Carsten" <Carsten_Schmid@mentor.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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 <564e45cb-8230-9c3d-24a8-b58e6e88349f@arm.com>
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From:   Valentin Schneider <valentin.schneider@arm.com>
Message-ID: <e6178a95-c02e-4fe9-49ee-7446e0d73882@arm.com>
Date:   Tue, 3 Dec 2019 11:09:25 +0000
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On 03/12/2019 10:40, Dietmar Eggemann wrote:
> On 03/12/2019 11:30, Valentin Schneider wrote:
>> On 03/12/2019 09:11, Schmid, Carsten wrote:
> 
> [...]
> 
>> That looks a lot like a recent issue we've had, see
>>
>>   https://lore.kernel.org/lkml/20191108131909.428842459@infradead.org/
>>
>> The issue is caused by
>>   
>>   67692435c411 ("sched: Rework pick_next_task() slow-path")
>>
>> which 5.4-rc2 has (without the fix which landed in -rc7) but 4.14 really
>> shouldn't, unless the kernel you're using has had core scheduling somehow
>> backported to it?
>>
>> I've only scraped the surface but I'd like to first ask: can you reproduce
>> the issue on v5.4 final ?
> 
> Can't be. 4.14.86 does not have ("sched: Rework pick_next_task()
> slow-path").
> 

Right, which is why I wondered if the kernel under test had had that 
backported to it for some reason (e.g. core scheduling). Peter pointed out
that this is a slightly different issue (nr_running matches the rbt), so
this is probably unrelated.