From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Rik van Riel <riel@surriel.com>
Subject: Re: sched: rq->nr_iowait transiently going negative after the recent p->on_cpu optimization
Date: Thu, 24 Sep 2020 10:27:51 -0400 [thread overview]
Message-ID: <20200924142751.GF4268@mtj.duckdns.org> (raw)
In-Reply-To: <20200924115042.GG2628@hirez.programming.kicks-ass.net>
Hello,
On Thu, Sep 24, 2020 at 01:50:42PM +0200, Peter Zijlstra wrote:
> Hurmph.. I suppose you're right :/ And this is an actual problem?
Yeah, this got exposed to userspace as a full 64bit number which overflowed
u32 conversion in the rust procfs library which aborted a program I was
working on multiple times over several months.
On a more theoretical side, it might also surprise nr_iowait_cpu() users.
However, a real problem that may be.
> I think the below should cure that, but blergh, not nice. If you could
> confirm, I'll try and think of something nicer.
Rik suggested that it'd be sufficient to return 0 on underflow especially
given that 0 is actually the right number to describe the state. So, maybe
that can be a nicer code-wise?
Thanks.
--
tejun
next prev parent reply other threads:[~2020-09-24 14:27 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-18 17:27 sched: rq->nr_iowait transiently going negative after the recent p->on_cpu optimization Tejun Heo
2020-09-24 11:50 ` Peter Zijlstra
2020-09-24 14:27 ` Tejun Heo [this message]
2020-09-24 14:50 ` Peter Zijlstra
2020-09-24 14:57 ` Tejun Heo
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