On Tue, 2006-09-12 at 05:05, Jan Kara wrote:
> Hi Andrew,
>
> here is the patch that came out of the thread "set_page_buffer_dirty
> should skip unmapped buffers". It fixes several flaws in the code
> writing out ordered data buffers during commit. It definitely fixed the
> problem Badari was seeing with fsx-linux test. Could you include it
> into -mm? Since there are quite complex interactions with other JBD code
> and the locking is kind of ugly, I'd leave it in -mm for a while whether
> some bug does not emerge ;). Thanks.
>
> Honza
I also worked on it because I didn't know you were working on it until I
located the root cause and tried to check bugzilla.
I reviewed your patch.
+ if (!inverted_lock(journal, bh)) {
+ jbd_lock_bh_state(bh);
+ spin_lock(&journal->j_list_lock);
+ }
Should journal->j_list_lock be unlocked before jbd_lock_bh_state(bh)?
The fsx-linux test issue is a race between journal_commit_transaction
and journal_dirty_data. After journal_commit_transaction adds buffer_head pointers
to wbuf, it might unlock journal->j_list_lock. Although all buffer head in wbuf are locked,
does that prevent journal_dirty_data from unlinking the buffer head from the transaction
and fsx-linux from truncating it?
I'm not a journal expert. But I want to discuss it.
My investigation is below (Scenario):
fsx-linux starts journal_dirty_data and journal_dirty_data links a jh to
journal->j_running_transaction's t_sync_datalist, kjournald might not
write the buffer to disk quickly, but saves it to array wbuf.
Then, fsx-linux starts the second journal_dirty_data of a new transaction
might submit the same buffer head and move the jh to the new transaction's
t_sync_datalist.
Then, fsx-linux truncates the last a couple of buffers of a page.
Then, block_write_full_page calls invalidatepage to invalidate the last a couple
of buffers of the page, so the journal_heads of the buffer_head are unlinked and
are marked as unmapped.
Then, fsx-linux extend the file and does a msync after changing the page content
by mmaping the page, so the page (inclduing the last buffer head) is marked dirty
again.
Then, kjournald's journal_commit_transaction goes through wbuf to submit_bh all
dirty buffers, but one buffer head is already marked as unmapped. A bug check is
triggerred.
>From above scenario, as long as the late calls doesn't try to lock the buffer head,
the race condition still exists.
I think the right way is to let journal_dirty_data to wait till wbuf is flushed.
Below is my patch. Any idea?
Signed-off-by: Zhang Yanmin <[email protected]>
---
diff -Nraup linux-2.6.18-rc7/fs/jbd/commit.c linux-2.6.18-rc7_jbd/fs/jbd/commit.c
--- linux-2.6.18-rc7/fs/jbd/commit.c 2006-09-20 08:57:12.000000000 +0800
+++ linux-2.6.18-rc7_jbd/fs/jbd/commit.c 2006-09-27 16:33:14.000000000 +0800
@@ -384,6 +384,8 @@ write_out_data:
spin_lock(&journal->j_list_lock);
}
+ wake_up(&journal->j_wait_commit_sync_datalist_free);
+
/*
* Wait for all previously submitted IO to complete.
*/
diff -Nraup linux-2.6.18-rc7/fs/jbd/journal.c linux-2.6.18-rc7_jbd/fs/jbd/journal.c
--- linux-2.6.18-rc7/fs/jbd/journal.c 2006-09-20 08:57:12.000000000 +0800
+++ linux-2.6.18-rc7_jbd/fs/jbd/journal.c 2006-09-27 16:11:27.000000000 +0800
@@ -656,6 +656,7 @@ static journal_t * journal_init_common (
init_waitqueue_head(&journal->j_wait_transaction_locked);
init_waitqueue_head(&journal->j_wait_logspace);
+ init_waitqueue_head(&journal->j_wait_commit_sync_datalist_free);
init_waitqueue_head(&journal->j_wait_done_commit);
init_waitqueue_head(&journal->j_wait_checkpoint);
init_waitqueue_head(&journal->j_wait_commit);
diff -Nraup linux-2.6.18-rc7/fs/jbd/transaction.c linux-2.6.18-rc7_jbd/fs/jbd/transaction.c
--- linux-2.6.18-rc7/fs/jbd/transaction.c 2006-09-20 08:57:12.000000000 +0800
+++ linux-2.6.18-rc7_jbd/fs/jbd/transaction.c 2006-09-28 14:42:05.000000000 +0800
@@ -965,6 +965,8 @@ int journal_dirty_data(handle_t *handle,
* never, ever allow this to happen: there's nothing we can do
* about it in this layer.
*/
+
+repeat_ifcase2:
jbd_lock_bh_state(bh);
spin_lock(&journal->j_list_lock);
if (jh->b_transaction) {
@@ -1032,6 +1034,32 @@ int journal_dirty_data(handle_t *handle,
time if it is redirtied */
}
+ if (jh->b_transaction != NULL &&
+ journal->j_committing_transaction ==
+ jh->b_transaction &&
+ jh->b_jlist == BJ_SyncData) {
+
+ wait_queue_head_t *queue_head;
+ spin_unlock(&journal->j_list_lock);
+ jbd_unlock_bh_state(bh);
+
+ if (need_brelse) {
+ BUFFER_TRACE(bh, "brelse");
+ __brelse(bh);
+ need_brelse = 0;
+ }
+
+ queue_head =
+ &journal->j_wait_commit_sync_datalist_free;
+ wait_event(*queue_head,
+ !(jh->b_transaction != NULL &&
+ journal->j_committing_transaction ==
+ jh->b_transaction &&
+ jh->b_jlist == BJ_SyncData));
+
+ goto repeat_ifcase2;
+ }
+
/* journal_clean_data_list() may have got there first */
if (jh->b_transaction != NULL) {
JBUFFER_TRACE(jh, "unfile from commit");
diff -Nraup linux-2.6.18-rc7/include/linux/jbd.h linux-2.6.18-rc7_jbd/include/linux/jbd.h
--- linux-2.6.18-rc7/include/linux/jbd.h 2006-09-20 08:57:13.000000000 +0800
+++ linux-2.6.18-rc7_jbd/include/linux/jbd.h 2006-09-27 16:29:47.000000000 +0800
@@ -583,6 +583,8 @@ struct transaction_s
* @j_wait_transaction_locked: Wait queue for waiting for a locked transaction
* to start committing, or for a barrier lock to be released
* @j_wait_logspace: Wait queue for waiting for checkpointing to complete
+ * @j_wait_commit_sync_datalist_free: Wait queue for waiting for commit
+ * transaction sync_datalist becomes null
* @j_wait_done_commit: Wait queue for waiting for commit to complete
* @j_wait_checkpoint: Wait queue to trigger checkpointing
* @j_wait_commit: Wait queue to trigger commit
@@ -686,6 +688,12 @@ struct journal_s
/* Wait queue for waiting for checkpointing to complete */
wait_queue_head_t j_wait_logspace;
+ /*
+ * Wait queue for waiting for commit transaction
+ * sync_datalist becomes null
+ */
+ wait_queue_head_t j_wait_commit_sync_datalist_free;
+
/* Wait queue for waiting for commit to complete */
wait_queue_head_t j_wait_done_commit;
-
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