On Mon, Jun 15, 2015 at 02:33:52PM +0200, Jan Kara wrote: > Yeah, that's nasty. Thanks for debugging this! However I think your fix > reintroduces the original deadlock issues. do_journal_get_write_access() > can end up blocking waiting for jbd2 thread to finish a commit while jbd2 > thread may be blocked waiting for the page to be unlocked. > > After some thought I don't think the deadlock is real since > do_journal_get_write_access() will currently only block if a buffer is > under writeout to the journal and at that point we don't wait for page > locks anymore. Also ext4_write_begin() does the same in data=journal mode > and we haven't observed deadlocks so far. But still things look really > fragile here. The reason why there are no deadlocks is the writeback in the commit thread happens when the inode gets written back --- but that only happens for data=ordered inodes, not data=journalled mode. I was a little worried about what might happen when after the 'j' chattr attribute gets set on an inode, and the inode was still on the ordered flush list. Hmm... I think we could also maybe fix this by having ext4_change_inode_journal_flag() force a journal commit before setting the JOURNAL_DATA flag. If we did that, we could just avoid dropping the page_lock in __ext4_journalled_writepage() altogether. What do you think? - 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
