Re: 2.6.18 ext3 panic.

Eric Sandeen
2006-10-12T20:07:38Z

Andrew Morton wrote:

> On Thu, 12 Oct 2006 14:28:20 +0200
> Jan Kara <jack@suse.cz> wrote:
>
>
>> Where can we call
>> journal_dirty_data() without PageLock?
>>
>
> block_write_full_page() will unlock the page, so ext3_writepage()
> will run journal_dirty_data_fn() against an unlocked page.
>
> I haven't looked into the exact details of the race, but it should
> be addressable via jbd_lock_bh_state() or j_list_lock coverage
I'm testing with something like this now; seem sane?

journal_dirty_data & journal_unmap_data both check do
jbd_lock_bh_state(bh) close to the top... journal_dirty_data_fn has checked
buffer_mapped before getting into journal_dirty_data, but that state may
change before the lock is grabbed. Similarly re-check after we drop the lock.

-Eric

Index: linux-2.6.18-1.2737.fc6/fs/jbd/transaction.c
===================================================================
--- linux-2.6.18-1.2737.fc6.orig/fs/jbd/transaction.c
+++ linux-2.6.18-1.2737.fc6/fs/jbd/transaction.c
@@ -967,6 +967,13 @@ int journal_dirty_data(handle_t *handle,
*/
jbd_lock_bh_state(bh);
spin_lock(&journal->j_list_lock);
+
+ /* Now that we have bh_state locked, are we really still mapped? */
+ if (!buffer_mapped(bh)) {
+ JBUFFER_TRACE(jh, "unmapped, bailing out");
+ goto no_journal;
+ }
+
if (jh->b_transaction) {
JBUFFER_TRACE(jh, "has transaction");
if (jh->b_transaction != handle->h_transaction) {
@@ -1028,6 +1036,11 @@ int journal_dirty_data(handle_t *handle,
sync_dirty_buffer(bh);
jbd_lock_bh_state(bh);
spin_lock(&journal->j_list_lock);
+ /* Since we dropped the lock... */
+ if (!buffer_mapped(bh)) {
+ JBUFFER_TRACE(jh, "Got unmapped");
+ goto no_journal;
+ }
/* The buffer may become locked again at any
time if it is redirtied */
}