On Sun, Aug 14, 2011 at 01:01:01PM -0700, Curt Wohlgemuth wrote: > > It seems that jh->b_transaction is NULL, and deferencing it to print > out jh->b_transaction->t_tid causes the NULL pointer deref. Hmm, if jh->b_transaction is null, then jbd2_journal_get_write_access() must not have been called on the journal_head. But the relevant code from ext4_journalled_writepage() is: ret = walk_page_buffers(handle, page_bufs, 0, len, NULL, do_journal_get_write_access); err = walk_page_buffers(handle, page_bufs, 0, len, NULL, write_end_fn); (write_end_fn is the function which calls which ultimately calls ext4_handle_dirty_metadata which then calls jbd2_journal_dirty_metadata(), which is where you're seeing the BUG_ON). I suspect what is going on is do_get_write_access() is returning an error, which means we never set jh->b_transaction. Hence when we call jbd2_journal_data_metadata(), we trigger the BUG. OK, what could cause do_get_write_access() to return an error? Two conditions: if the handle is aborted (due to a previous error), in which case it returns -EROFS, or if it can't get the memory needed make a copy of the buffer, in which case there should have been a "do_get_write_access: OOM for frozen buffer" error message earlier in the log. (No, it's not prefixed with JBD2 --- it probably should be.) Any chance you're seeing any indication of either possibility in the messages before the BUG message? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
