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

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Message-ID: <ZjzsC8KwEoDzAZBt@fedora>
Date: Thu, 9 May 2024 23:30:19 +0800
From: Baoquan He <bhe@...hat.com>
To: Rik van Riel <riel@...riel.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 05/09/24 at 09:41am, Rik van Riel wrote:
> 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.

OK, thanks for the explanation.

Acked-by: Baoquan He <bhe@...hat.com>