linux-kernel - Re: [PATCH] writeback: guard against jiffies wraparound on inode->dirtied

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Date:	Wed, 01 Apr 2009 22:22:06 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, fengguang.wu@...el.com
Subject: Re: [PATCH] writeback: guard against jiffies wraparound on inode->dirtied_when checks (try #3)

Jeff Layton <jlayton@...hat.com> writes:
>
> The problem is that these checks assume that dirtied_when is updated
> periodically. If an inode is continuously being used for I/O it can be
> persistently marked as dirty and will continue to age. Once the time
> difference between dirtied_when and the jiffies value it is being
> compared to is greater than or equal to half the maximum of the jiffies
> type, the logic of the time_*() macros inverts and the opposite of what
> is needed is returned. On 32-bit architectures that's just under 25 days
> (assuming HZ == 1000).

I wonder if this can happen in other places using jiffies time stamp
too. Why not? Perhaps that check macro should be in timer.h and some auditing done
over the whiole code base?

-Andi


-- 
ak@...ux.intel.com -- Speaking for myself only.
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