From bdb76ef5a4bc8676a81034a443f1eda450b4babb Mon Sep 17 00:00:00 2001 From: Zach Brown Date: Tue, 30 Oct 2007 11:45:46 -0700 Subject: 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 --- mm/filemap.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) (limited to 'mm') diff --git a/mm/filemap.c b/mm/filemap.c index 7c8643630023..9940895f734c 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2511,21 +2511,17 @@ generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, } retval = mapping->a_ops->direct_IO(rw, iocb, iov, offset, nr_segs); - if (retval) - goto out; /* * Finally, try again to invalidate clean pages which might have been - * faulted in by get_user_pages() if the source of the write was an - * mmap()ed region of the file we're writing. That's a pretty crazy - * thing to do, so we don't support it 100%. If this invalidation - * fails and we have -EIOCBQUEUED we ignore the failure. + * cached by non-direct readahead, or faulted in by get_user_pages() + * if the source of the write was an mmap'ed region of the file + * we're writing. Either one is a pretty crazy thing to do, + * so we don't support it 100%. If this invalidation + * fails, tough, the write still worked... */ if (rw == WRITE && mapping->nrpages) { - int err = invalidate_inode_pages2_range(mapping, - offset >> PAGE_CACHE_SHIFT, end); - if (err && retval >= 0) - retval = err; + invalidate_inode_pages2_range(mapping, offset >> PAGE_CACHE_SHIFT, end); } out: return retval; -- cgit v1.2.1