From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH] writeback: guard against jiffies wraparound on inode->dirtied_when checks (try #2) Date: Tue, 31 Mar 2009 17:20:31 -0700 Message-ID: <20090331172031.b2971f1e.akpm@linux-foundation.org> References: <1238544239-31882-1-git-send-email-jlayton@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Jeff Layton Return-path: In-Reply-To: <1238544239-31882-1-git-send-email-jlayton@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, 31 Mar 2009 20:03:59 -0400 Jeff Layton wrote: > + * It's not sufficient to just do a time_after() check on > + * dirtied_when. That assumes that dirtied_when will always > + * change within a period of jiffies that encompasses half the > + * machine word size (2^31 jiffies on 32-bit arch). That's not > + * necessarily the case if an inode is being constantly > + * redirtied. Since dirtied_when can never be in the future, > + * we can assume that if it appears to be so then it is > + * actually in the distant past. so this really is a 32-bit-only thing. I guess that isn't worth optimising for though. otoh, given that all three comparisons are the same: + time_after(inode->dirtied_when, *older_than_this) && + time_before_eq(inode->dirtied_when, jiffies)) (although one is inverted (i think?)), it might end up nicer if this was all done in a little helper function? That way we only need to comment what's going on at a single site, and we could omit the additional test if !CONFIG_64BIT.