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Message-ID: <47225835.4050309@datallegro.com> Date: Fri, 26 Oct 2007 17:12:21 -0400 From: Karl Schendel <kschendel@...allegro.com> To: linux-kernel@...r.kernel.org CC: torvalds@...ux-foundation.org Subject: [PATCH] Fix bad data from non-direct-io read after direct-io write This patch fixes a race between direct IO writes and non-direct IO reads on the same file. The symptom is a stale file page seen by any non-direct-IO reader, which persists until the page is invalidated somehow (e.g. page rewritten again, or memory pressure, or reboot). An improper return test caused direct-IO's after-write page invalidations to be skipped. If we're writing page N, and the reader is reading page N-x for small x, and the read code decides to readahead, it's not too hard to cause a race that leaves an old, stale copy of the page in the page cache. Retval is usually +nonzero after the mapping->a_ops->direct_IO call! Signed-off-by: Karl Schendel <kschendel@...allegro.com> --- By the way, I agree that the userland situation is stupid, and I'm addressing that in the application (happens to be the Ingres DBMS). However, the kernel shouldn't compound the stupidity. I'll try to watch for replies, but it would be very useful to cc me at kschendel@...allegro.com if any discussion is needed; I'm not subscribed to lkml. --- linux-2.6.23.1-base/mm/filemap.c 2007-10-12 12:43:44.000000000 -0400 +++ linux-2.6.23.1/mm/filemap.c 2007-10-26 16:12:08.000000000 -0400 @@ -2194,7 +2194,7 @@ generic_file_direct_IO(int rw, struct ki } retval = mapping->a_ops->direct_IO(rw, iocb, iov, offset, nr_segs); - if (retval) + if (retval < 0) goto out; /* - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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