From: Zach Brown Date: Tue, 30 Oct 2007 18:45:46 +0000 (-0700) Subject: dio: fix cache invalidation after sync writes X-Git-Tag: v2.6.24-rc2~73 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bdb76ef5a4bc8676a81034a443f1eda450b4babb;p=pandora-kernel.git dio: fix cache invalidation after sync writes Commit commit 65b8291c4000e5f38fc94fb2ca0cb7e8683c8a1b ("dio: invalidate clean pages before dio write") introduced a bug which stopped dio from ever invalidating the page cache after writes. It still invalidated it before writes so most users were fine. Karl Schendel reported ( http://lkml.org/lkml/2007/10/26/481 ) hitting this bug when he had a buffered reader immediately reading file data after an O_DIRECT wirter had written the data. The kernel issued read-ahead beyond the position of the reader which overlapped with the O_DIRECT writer. The failure to invalidate after writes caused the reader to see stale data from the read-ahead. The following patch is originally from Karl. The following commentary is his: The below 3rd try takes on your suggestion of just invalidating no matter what the retval from the direct_IO call. I ran it thru the test-case several times and it has worked every time. The post-invalidate is probably still too early for async-directio, but I don't have a testcase for that; just sync. And, this won't be any worse in the async case. I added a test to the aio-dio-regress repository which mimics Karl's IO pattern. It verifed the bad behaviour and that the patch fixed it. I agree with Karl, this still doesn't help the case where a buffered reader follows an AIO O_DIRECT writer. That will require a bit more work. This gives up on the idea of returning EIO to indicate to userspace that stale data remains if the invalidation failed. Signed-off-by: Zach Brown Cc: Karl Schendel Cc: Benjamin LaHaise Cc: Andrew Morton Cc: Nick Piggin Cc: Leonid Ananiev Cc: Chris Mason Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed