linux-kernel - Re: [PATCH] fs/proc: fix softlockup in __read

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Date: Thu, 09 May 2024 09:41:27 -0400
From: Rik van Riel <riel@...riel.com>
To: Baoquan He <bhe@...hat.com>
Cc: akpm@...ux-foundation.org, Vivek Goyal <vgoyal@...hat.com>, Dave Young
 <dyoung@...hat.com>, kexec@...ts.infradead.org,
 linux-kernel@...r.kernel.org,  linux-fsdevel@...r.kernel.org,
 kernel-team@...a.com
Subject: Re: [PATCH] fs/proc: fix softlockup in __read_vmcore

On Thu, 2024-05-09 at 11:52 +0800, Baoquan He wrote:
> Hi,
> 
> On 05/07/24 at 09:18am, Rik van Riel wrote:
> > While taking a kernel core dump with makedumpfile on a larger
> > system,
> > softlockup messages often appear.
> > 
> > While softlockup warnings can be harmless, they can also interfere
> > with things like RCU freeing memory, which can be problematic when
> > the kdump kexec image is configured with as little memory as
> > possible.
> > 
> > Avoid the softlockup, and give things like work items and RCU a
> > chance to do their thing during __read_vmcore by adding a
> > cond_resched.
> 
> Thanks for fixing this.
> 
> By the way, is it easy to reproduce? And should we add some trace of
> the
> softlockup into log so that people can search for it and confirm when
> encountering it?

It is pretty easy to reproduce, but it does not happen all the time.
With millions of systems, even rare errors are common :)

However, we have been running with this fix for long enough (we
deployed it in order to test it) that I don't think we have the 
warning stored any more. Those logs were rotated out long ago.

kind regards,

Rik
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