linux-kernel - Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

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Message-ID: <20210308064558.GA3617@hori.linux.bs1.fc.nec.co.jp>
Date:   Mon, 8 Mar 2021 06:45:58 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     "Luck, Tony" <tony.luck@...el.com>
CC:     Aili Yao <yaoaili@...gsoft.com>,
        Oscar Salvador <osalvador@...e.de>,
        "david@...hat.com" <david@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "yangfeng1@...gsoft.com" <yangfeng1@...gsoft.com>
Subject: Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

On Fri, Mar 05, 2021 at 02:11:43PM -0800, Luck, Tony wrote:
> This whole page table walking patch is trying to work around the
> races caused by multiple calls to memory_failure() for the same
> page.
> 
> Maybe better to just avoid the races.  The comment right above
> memory_failure says:
> 
>  * Must run in process context (e.g. a work queue) with interrupts
>  * enabled and no spinlocks hold.
> 
> So it should be safe to grab and hold a mutex.  See patch below.

The mutex approach looks simpler and safer, so I'm fine with it.

> 
> -Tony
> 
> commit 8dd0dbe7d595e02647e9c2c76c03341a9f6bd7b9
> Author: Tony Luck <tony.luck@...el.com>
> Date:   Fri Mar 5 10:40:48 2021 -0800
> 
>     Use a mutex to avoid memory_failure() races
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 24210c9bd843..c1509f4b565e 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1381,6 +1381,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  	return rc;
>  }
>  
> +static DEFINE_MUTEX(mf_mutex);
> +
>  /**
>   * memory_failure - Handle memory failure of a page.
>   * @pfn: Page Number of the corrupted page
> @@ -1424,12 +1426,18 @@ int memory_failure(unsigned long pfn, int flags)
>  		return -ENXIO;
>  	}
>  
> +	mutex_lock(&mf_mutex);

Is it better to take mutex before memory_failure_dev_pagemap() block?
Or we don't have to protect against race for device memory?

Thanks,
Naoya Horiguchi