At 16:16 08/08/19, Andrew Morton wrote:
>On Tue, 19 Aug 2008 16:03:45 +0900 Hisashi Hifumi
><hifumi.hisashi@xxxxxxxxxxxxx> wrote:
>
>>
>> At 21:59 08/08/13, Chris Mason wrote:
>> >On Wed, 2008-08-13 at 12:16 +0200, Jan Kara wrote:
>> >
>> >> > With that said, I don't have strong feelings against falling back to
>> >> > buffered IO when the invalidate fails. Maybe Zach remembers something I
>> >> > don't?
>> >> I don't have a strong opinion either. Falling back to buffered writes is
>> >> simpler at least for ext3/ext4 because properly synchronizing against
>> >> writepage() call does not seem to have a nice solution either in
>> >> do_launder_page() or in releasepage(). OTOH is hides the fact the invalidate
>> >> is failing and so if we screw up something in future and it fails often, it
>> >> might be hard to notice / track down the performance penalty.
>> >
>> >In general, these races don't happen often, and when they do it is
>> >because someone is mixing page cache and O_DIRECT io to the same file.
>> >That is explicitly outside the main use case of O_DIRECT.
>> >
>> >So, I'd rather see us slow down O_DIRECT in the mixed use case than have
>> >big impacts in complexity or speed to other parts of the kernel. If
>> >falling back avoids problems in some filesystems or avoids clearing the
>> >uptodate bit unexpectedly, I'd much rather take the fallback patch.
>> >
>> >-chris
>>
>> Hi Andrew.
>> I think we don't have strong feelings against falling back to buffered
>writes to
>> fix the direct-io -EIO problem.
>>
>> Please review my patch.
>>
>
>umm, what problem does it solve?
>
>If I recall correctly, we had a problem with pages which are pinned by
>an ext3 transaction, and those pages weren't releaseable for direct-io,
>and this caused some problem?
Sorry, I should describe about this problem.
Yes, Dio write returns EIO when try_to_release_page fails because sometimes
bh is still referenced by jbd or other place.
The race between freeing buffer and committing transaction(jbd) was fixed
but I found another race. We have been discussing about this issue, and
I proposed that falling back to buffered writes to fix this issue.
I think we don't have strong feelings against falling back to buffered
writes to fix the direct-io -EIO problem.
>
>I think falling back to buffered writes is always a safe course, but
>it'd be nice to have a full description of the change, please.
[PATCH] VFS: fix dio write returning EIO when try_to_release_page fails
Dio write returns EIO when try_to_release_page fails because bh is
still referenced.
The patch
"commit 3f31fddfa26b7594b44ff2b34f9a04ba409e0f91
Author: Mingming Cao <cmm@xxxxxxxxxx>
Date: Fri Jul 25 01:46:22 2008 -0700
jbd: fix race between free buffer and commit transaction
"
was merged into 2.6.27-rc1, but I noticed that this patch is not enough
to fix the race.
I did fsstress test heavily to 2.6.27-rc1, and found that dio write still
sometimes got EIO through this test.
The patch above fixed race between freeing buffer(dio) and committing
transaction(jbd) but I discovered that there is another race,
freeing buffer(dio) and ext3/4_ordered_writepage.
: background_writeout()
->write_cache_pages()
->ext3_ordered_writepage()
walk_page_buffers() -> take a bh ref
block_write_full_page() -> unlock_page
: <- end_page_writeback
: <- race! (dio write->try_to_release_page fails)
walk_page_buffers() ->release a bh ref
ext3_ordered_writepage holds bh ref and does unlock_page remaining
taking a bh ref, so this causes the race and failure of
try_to_release_page.
To fix this race, I used the approach of falling back to buffered writes
if try_to_release_page fails on a page.
Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx>
diff -Nrup linux-2.6.27-rc3.org/mm/filemap.c linux-2.6.27-rc3/mm/filemap.c
--- linux-2.6.27-rc3.org/mm/filemap.c 2008-08-13 13:48:47.000000000 +0900
+++ linux-2.6.27-rc3/mm/filemap.c 2008-08-19 15:45:31.000000000 +0900
@@ -2129,13 +2129,20 @@ generic_file_direct_write(struct kiocb *
* After a write we want buffered reads to be sure to go to disk to get
* the new data. We invalidate clean cached page from the region we're
* about to write. We do this *before* the write so that we can return
- * -EIO without clobbering -EIOCBQUEUED from ->direct_IO().
+ * without clobbering -EIOCBQUEUED from ->direct_IO().
*/
if (mapping->nrpages) {
written = invalidate_inode_pages2_range(mapping,
pos >> PAGE_CACHE_SHIFT, end);
- if (written)
+ /*
+ * If a page can not be invalidated, return 0 to fall back
+ * to buffered write.
+ */
+ if (written) {
+ if (written == -EBUSY)
+ return 0;
goto out;
+ }
}
written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
diff -Nrup linux-2.6.27-rc3.org/mm/truncate.c linux-2.6.27-rc3/mm/truncate.c
--- linux-2.6.27-rc3.org/mm/truncate.c 2008-08-13 13:48:48.000000000 +0900
+++ linux-2.6.27-rc3/mm/truncate.c 2008-08-19 12:10:46.000000000 +0900
@@ -380,7 +380,7 @@ static int do_launder_page(struct addres
* Any pages which are found to be mapped into pagetables are unmapped prior to
* invalidation.
*
- * Returns -EIO if any pages could not be invalidated.
+ * Returns -EBUSY if any pages could not be invalidated.
*/
int invalidate_inode_pages2_range(struct address_space *mapping,
pgoff_t start, pgoff_t end)
@@ -440,7 +440,7 @@ int invalidate_inode_pages2_range(struct
ret2 = do_launder_page(mapping, page);
if (ret2 == 0) {
if (!invalidate_complete_page2(mapping, page))
- ret2 = -EIO;
+ ret2 = -EBUSY;
}
if (ret2 < 0)
ret = ret2;
--
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