linux-kernel - Re: [PATCH] mm: clean up hwpoison page cache page in fault path

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Date:   Sat, 12 Feb 2022 11:10:47 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Rik van Riel <riel@...riel.com>
CC:     <kernel-team@...com>, <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: clean up hwpoison page cache page in fault path

On 2022/2/12 6:05, Rik van Riel wrote:
> Sometimes the page offlining code can leave behind a hwpoisoned clean
> page cache page. This can lead to programs being killed over and over

Yep, __soft_offline_page tries to invalidate_inode_page in a lightway.

> and over again as they fault in the hwpoisoned page, get killed, and
> then get re-spawned by whatever wanted to run them.
>     
> This is particularly embarrassing when the page was offlined due to
> having too many corrected memory errors. Now we are killing tasks
> due to them trying to access memory that probably isn't even corrupted.
>     
> This problem can be avoided by invalidating the page from the page
> fault handler, which already has a branch for dealing with these
> kinds of pages. With this patch we simply pretend the page fault
> was successful if the page was invalidated, return to userspace,
> incur another page fault, read in the file from disk (to a new
> memory page), and then everything works again.
>     
> Signed-off-by: Rik van Riel <riel@...riel.com>

Good catch! This looks good to me. Thanks.

Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

> 
> diff --git a/mm/memory.c b/mm/memory.c
> index c125c4969913..2300358e268c 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3871,11 +3871,16 @@ static vm_fault_t __do_fault(struct vm_fault *vmf)
>  		return ret;
>  
>  	if (unlikely(PageHWPoison(vmf->page))) {
> -		if (ret & VM_FAULT_LOCKED)
> +		int poisonret = VM_FAULT_HWPOISON;
> +		if (ret & VM_FAULT_LOCKED) {
> +			/* Retry if a clean page was removed from the cache. */
> +			if (invalidate_inode_page(vmf->page))
> +				poisonret = 0;
>  			unlock_page(vmf->page);
> +		}
>  		put_page(vmf->page);
>  		vmf->page = NULL;
> -		return VM_FAULT_HWPOISON;
> +		return poisonret;
>  	}
>  
>  	if (unlikely(!(ret & VM_FAULT_LOCKED)))
> 
>