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dio: fix cache invalidation after sync writes

Browse source 
Commit commit 65b8291c40 ("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>
This commit is contained in:
Zach Brown 2007-10-30 11:45:46 -07:00 committed by Linus Torvalds
parent e58b7dab27
commit bdb76ef5a4
1 changed files with 6 additions and 10 deletions
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16
mm/filemap.c
View file

@ -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;