linux-kernel - Re: [PATCH 2/2 v2] mm: print out information of file affected by memory error

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Message-Id: <20121105140154.fce89f05.akpm@linux-foundation.org>
Date:	Mon, 5 Nov 2012 14:01:54 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Tony Luck <tony.luck@...el.com>, Andi Kleen <andi.kleen@...el.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 2/2 v2] mm: print out information of file affected by
 memory error

On Fri,  2 Nov 2012 12:33:13 -0400
Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:

> Printing out the information about which file can be affected by a
> memory error in generic_error_remove_page() is helpful for user to
> estimate the impact of the error.
> 
> Changelog v2:
>   - dereference mapping->host after if (!mapping) check for robustness
> 
> ...
>
> --- v3.7-rc3.orig/mm/truncate.c
> +++ v3.7-rc3/mm/truncate.c
> @@ -151,14 +151,20 @@ int truncate_inode_page(struct address_space *mapping, struct page *page)
>   */
>  int generic_error_remove_page(struct address_space *mapping, struct page *page)
>  {
> +	struct inode *inode;
> +
>  	if (!mapping)
>  		return -EINVAL;
> +	inode = mapping->host;
>  	/*
>  	 * Only punch for normal data pages for now.
>  	 * Handling other types like directories would need more auditing.
>  	 */
> -	if (!S_ISREG(mapping->host->i_mode))
> +	if (!S_ISREG(inode->i_mode))
>  		return -EIO;
> +	pr_info("MCE %#lx: file info pgoff:%lu, inode:%lu, dev:%s\n",
> +		page_to_pfn(page), page_index(page),
> +		inode->i_ino, inode->i_sb->s_id);
>  	return truncate_inode_page(mapping, page);
>  }
>  EXPORT_SYMBOL(generic_error_remove_page);

A couple of things.

- I worry that if a hardware error occurs, it might affect a large
  amount of memory all at the same time.  For example, if a 4G memory
  block goes bad, this message will be printed a million times?

- hard-wiring "MCE" in here seems a bit of a layering violation? 
  What right does the generic, core .error_remove_page() implementation
  have to assume that it was called because of an MCE?  Many CPU types
  don't eveh have such a thing?

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