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Date: Thu, 9 May 2024 11:52:56 +0800
From: Baoquan He <bhe@redhat.com>
To: Rik van Riel <riel@surriel.com>
Cc: akpm@linux-foundation.org, Vivek Goyal <vgoyal@redhat.com>,
	Dave Young <dyoung@redhat.com>, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	kernel-team@meta.com
Subject: Re: [PATCH] fs/proc: fix softlockup in __read_vmcore
Message-ID: <ZjxImBiQ+niK1PEw@MiWiFi-R3L-srv>
References: <20240507091858.36ff767f@imladris.surriel.com>
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In-Reply-To: <20240507091858.36ff767f@imladris.surriel.com>

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?

Thanks
Baoquan

> ---
>  fs/proc/vmcore.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 1fb213f379a5..d06607a1f137 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -383,6 +383,8 @@ static ssize_t __read_vmcore(struct iov_iter *iter, loff_t *fpos)
>  		/* leave now if filled buffer already */
>  		if (!iov_iter_count(iter))
>  			return acc;
> +
> +		cond_resched();
>  	}
>  
>  	list_for_each_entry(m, &vmcore_list, list) {
> -- 
> 2.42.0
> 
> 
> 
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