On Wed 13-03-13 18:52:33, Zheng Liu wrote: > On Wed, Mar 13, 2013 at 10:15:11AM +0100, Jan Kara wrote: > [snip] > > > > I post the sysrq-w output here. But IMHO it is not very useful. So I > > > > also post the sysrq-t output. > > > Heh, curious. Thanks for the data. So worker thinks there's nothing to do > > > but inode has elevated i_ioend_count... Maybe we leaked ioend somewhere. > > > I'll check the code when I have time. > > Ah, I think I see what's going on. > > a) Code in ext4_ext_direct_IO() is racy wrt iocb->private handling (that > > can get cleared concurrently from ext4_end_io_dio()). > > Thanks for tracing this problem. But I am still confused that iocb is > allocated on stack in do_sync_write(), and is allocated from slab in > ioctx_alloc(). You mean iocb in ext4_ext_direct_IO and ext4_end_io_dio > is the same one? Yes, it is. > Then this iocb could be changed concurrently, and we are blocked for more > than 120s. I must miss something. Well, the hang results from direct IO code forgetting to call ext4_free_io_end() in some (likely error recovery) path. So inode->i_ioend_count remains elevated and we never finish waiting in ext4_evict_inode(). How that forgotten ext4_free_io_end() really happens isn't 100% clear to me but I really suspect something with concurrent iocb modification goes wrong... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
