From bdb76ef5a4bc8676a81034a443f1eda450b4babb Mon Sep 17 00:00:00 2001
From: Zach Brown <zach.brown@oracle.com>
Date: Tue, 30 Oct 2007 11:45:46 -0700
Subject: [PATCH] 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 <zach.brown@oracle.com>
Cc: Karl Schendel <kschendel@datallegro.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Leonid Ananiev <leonid.i.ananiev@linux.intel.com>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/filemap.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 7c8643630023d2..9940895f734ccd 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;
--
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