From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 26 Jan 2008 22:03:56 -0800 From: Andrew Morton Subject: Re: [patch] mm: fix PageUptodate data race Message-Id: <20080126220356.0b77f0e9.akpm@linux-foundation.org> In-Reply-To: <20080122040114.GA18450@wotan.suse.de> References: <20080122040114.GA18450@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: hugh@veritas.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: > On Tue, 22 Jan 2008 05:01:14 +0100 Nick Piggin wrote: > > After running SetPageUptodate, preceeding stores to the page contents to > actually bring it uptodate may not be ordered with the store to set the page > uptodate. > > Therefore, another CPU which checks PageUptodate is true, then reads the > page contents can get stale data. > > Fix this by having an smp_wmb before SetPageUptodate, and smp_rmb after > PageUptodate. > > Many places that test PageUptodate, do so with the page locked, and this > would be enough to ensure memory ordering in those places if SetPageUptodate > were only called while the page is locked. Unfortunately that is not always > the case for some filesystems, but it could be an idea for the future. > > Also bring the handling of anonymous page uptodateness in line with that of > file backed page management, by marking anon pages as uptodate when they _are_ > uptodate, rather than when our implementation requires that they be marked as > such. Doing allows us to get rid of the smp_wmb's in the page copying > functions, which were especially added for anonymous pages for an analogous > memory ordering problem. Both file and anonymous pages are handled with the > same barriers. > So... it's two patches in one. What kernel is this against? Looks like mainline. Is it complete and correct when applied against the large number of pending MM changes? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org