Hi
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.
Following patch fixes this race.
Thanks.
Signed-off-by :Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx>
diff -Nrup linux-2.6.27-rc1.org/fs/jbd/transaction.c linux-2.6.27-rc1/fs/jbd/transaction.c
--- linux-2.6.27-rc1.org/fs/jbd/transaction.c 2008-07-29 19:28:47.000000000 +0900
+++ linux-2.6.27-rc1/fs/jbd/transaction.c 2008-07-29 20:40:12.000000000 +0900
@@ -1764,6 +1764,12 @@ int journal_try_to_free_buffers(journal_
*/
if (ret == 0 && (gfp_mask & __GFP_WAIT) && (gfp_mask & __GFP_FS)) {
journal_wait_for_transaction_sync_data(journal);
+
+ bh = head;
+ do {
+ while (atomic_read(&bh->b_count))
+ schedule();
+ } while ((bh = bh->b_this_page) != head);
ret = try_to_free_buffers(page);
}
diff -Nrup linux-2.6.27-rc1.org/fs/jbd2/transaction.c linux-2.6.27-rc1/fs/jbd2/transaction.c
--- linux-2.6.27-rc1.org/fs/jbd2/transaction.c 2008-07-29 19:28:47.000000000 +0900
+++ linux-2.6.27-rc1/fs/jbd2/transaction.c 2008-07-29 20:56:42.000000000 +0900
@@ -1583,6 +1583,12 @@ int jbd2_journal_try_to_free_buffers(jou
*/
if (ret == 0 && (gfp_mask & __GFP_WAIT) && (gfp_mask & __GFP_FS)) {
jbd2_journal_wait_for_transaction_sync_data(journal);
+
+ bh = head;
+ do {
+ while (atomic_read(&bh->b_count))
+ schedule();
+ } while ((bh = bh->b_this_page) != head);
ret = try_to_free_buffers(page);
}
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