On 2017/12/8 13:36, Ben Hutchings wrote: > On Fri, 2017-12-08 at 12:03 +0800, alex chen wrote: >> >> On 2017/12/8 10:26, Ben Hutchings wrote: >>> On Fri, 2017-12-08 at 08:39 +0800, alex chen wrote: >>>> >>>> On 2017/12/8 2:25, Ben Hutchings wrote: >>>>> On Wed, 2017-12-06 at 09:02 +0800, alex chen wrote: >>>>>> Hi Ben, >>>>>> >>>>>> Thanks for your reply. >>>>>> >>>>>> On 2017/12/5 23:49, Ben Hutchings wrote: >>>>>>> On Wed, 2017-11-22 at 11:12 +0100, Greg Kroah-Hartman wrote: >>>>>>>> 4.4-stable review patch. If anyone has any objections, >>>>>>>> please let me know. >>>>>>>> >>>>>>>> ------------------ >>>>>>>> >>>>>>>> From: alex chen <alex.chen@xxxxxxxxxx> >>>>>>>> >>>>>>>> commit 28f5a8a7c033cbf3e32277f4cc9c6afd74f05300 upstream. >>>>>>>> >>>>>>>> we should wait dio requests to finish before inode lock in >>>>>>>> ocfs2_setattr(), otherwise the following deadlock will >>>>>>>> happen: >>>>>>> >>>>>>> [...] >>>>>>> >>>>>>> I looked at the kernel-doc for inode_dio_wait(): >>>>>>> >>>>>>> /** >>>>>>> * inode_dio_wait - wait for outstanding DIO requests to finish >>>>>>> * @inode: inode to wait for >>>>>>> * >>>>>>> * Waits for all pending direct I/O requests to finish so that we can >>>>>>> * proceed with a truncate or equivalent operation. >>>>>>> * >>>>>>> * Must be called under a lock that serializes taking new references >>>>>>> * to i_dio_count, usually by inode->i_mutex. >>>>>>> */ >>>>>>> >>>>>>> Now that ocfs2_setattr() calls this outside of the inode locked region, >>>>>>> what prevents another task adding a new dio request immediately >>>>>>> afterward? >>>>>>> >>>>>> >>>>>> In the kernel 4.6, firstly, we use the inode_lock() in do_truncate() to >>>>>> prevent another bio to be issued from this node. >>>>> >>>>> [...] >>>>> >>>>> Yes but there seems to be a race condition - after the call to >>>>> inode_dio_wait() and before the call to inode_lock(), another dio >>>>> request can be added. >>> >>> Sorry, I've been mixing up inode_lock() and ocfs2_inode_lock(). >>> However: >>> >>>> In the truncating file situation, the lock order is as follow: >>>> do_truncate() >>>> inode_lock() >>>> notify_change() >>>> ocfs2_setattr() >>>> inode_dio_wait() >>>> --here it is under the protect of inode_lock(), so another dio requests >>>> from another process will not be added. >>> >>> only DIO reads seem to take the inode lock. >>> >> >> I do not clearly understand what you mean. >> The inode_lock() will be called in ocfs2_file_write_iter(). > > Oh I see. I didn't realise that was part of the call chain. > >> You mean only DIO writes seem to take the inode_lock()? > > I did mean reads, as do_blockdev_direct_IO() may call inode_lock() for > reads - but ocfs2 doesn't set the flag for that. Maybe that's OK? I think you are right, we should set the DIO_LOCKING flag in ocfs2_direct_IO(). Thanks, Alex > >> BTW, in this patch, I just adjusted the inode_dio_wait() to the front of the ocfs2_rw_lock() >> and didn't adjust the order of inode_lock() and inode_dio_wait(). > > Right. I think you've convinced me to stop worrying about this. > > Ben. >