linux-kernel - Re: [PATCH] [16/19] HWPOISON: Enable .remove_error

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Date:	Wed, 5 Aug 2009 19:52:42 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, "tytso@....edu" <tytso@....edu>,
	"mfasheh@...e.com" <mfasheh@...e.com>,
	"aia21@...tab.net" <aia21@...tab.net>,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
	"swhiteho@...hat.com" <swhiteho@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"hidehiro.kawai.ez@...achi.com" <hidehiro.kawai.ez@...achi.com>
Subject: Re: [PATCH] [16/19] HWPOISON: Enable .remove_error_page for
	migration aware file systems

On Wed, Aug 05, 2009 at 07:12:31PM +0800, Christoph Hellwig wrote:
> On Wed, Aug 05, 2009 at 11:36:43AM +0200, Andi Kleen wrote:
> > 
> > Enable removing of corrupted pages through truncation
> > for a bunch of file systems: ext*, xfs, gfs2, ocfs2, ntfs
> > These should cover most server needs.
> > 
> > I chose the set of migration aware file systems for this
> > for now, assuming they have been especially audited.
> > But in general it should be safe for all file systems
> > on the data area that support read/write and truncate.
> > 
> > Caveat: the hardware error handler does not take i_mutex
> > for now before calling the truncate function. Is that ok?
> 
> It will probably need locking, e.g. the iolock in XFS.  I'll
> need to take a look at the actual implementation of
> generic_error_remove_page to make sense of this.

In patch 13, it simply calls truncate_inode_page() for S_ISREG inodes.

Nick suggests call truncate_inode_page() with i_mutex. Sure we can
do mutex_trylock(i_mutex), but we'd appreciate it if some fs gurus
can demonstrate some bad consequences of not doing so, thanks!

> Is there any way for us to test this functionality without introducing
> real hardware problems?

We have some additional patches (ugly but works for now) that export
interfaces for injecting hwpoison to selected types pages. It can
guarantee only data/metadata pages of selected fs will be poisoned.
Based on which we can do all kinds of stress testing in user space.

Thanks,
Fengguang
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