linux-kernel - Re: [PATCH v5 1/3] mm/memory-failure: Use a mutex to avoid memory

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Message-ID: <20210524084232.GA3203898@hori.linux.bs1.fc.nec.co.jp>
Date:   Mon, 24 May 2021 08:42:33 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Naoya Horiguchi <nao.horiguchi@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Tony Luck <tony.luck@...el.com>,
        Aili Yao <yaoaili@...gsoft.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>, Jue Wang <juew@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/3] mm/memory-failure: Use a mutex to avoid
 memory_failure() races

On Sat, May 22, 2021 at 03:09:00PM -0700, Andrew Morton wrote:
> On Fri, 21 May 2021 12:01:54 +0900 Naoya Horiguchi <nao.horiguchi@...il.com> wrote:
> 
> > There can be races when multiple CPUs consume poison from the same
> > page. The first into memory_failure() atomically sets the HWPoison
> > page flag and begins hunting for tasks that map this page. Eventually
> > it invalidates those mappings and may send a SIGBUS to the affected
> > tasks.
> > 
> > But while all that work is going on, other CPUs see a "success"
> > return code from memory_failure() and so they believe the error
> > has been handled and continue executing.
> > 
> > Fix by wrapping most of the internal parts of memory_failure() in
> > a mutex.
> 
> We can reduce the scope of that mutex, which helps readability at least.

Thanks, this change is totally fine to me.

> 
> --- a/mm/memory-failure.c~mm-memory-failure-use-a-mutex-to-avoid-memory_failure-races-fix
> +++ a/mm/memory-failure.c
> @@ -1397,8 +1397,6 @@ out:
>  	return rc;
>  }
>  
> -static DEFINE_MUTEX(mf_mutex);
> -
>  /**
>   * memory_failure - Handle memory failure of a page.
>   * @pfn: Page Number of the corrupted page
> @@ -1425,6 +1423,7 @@ int memory_failure(unsigned long pfn, in
>  	int res = 0;
>  	unsigned long page_flags;
>  	bool retry = true;
> +	static DEFINE_MUTEX(mf_mutex);
>  
>  	if (!sysctl_memory_failure_recovery)
>  		panic("Memory failure on page %lx", pfn);
> _
>