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(). You mean only DIO writes seem to take the inode_lock()? 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(). Thanks, Alex > Ben. > >> ocfs2_rw_lock() >> ocfs2_inode_lock_tracker() >> this function is used to prevent the inode from being modified by another >> nodes in the cluster >> inode_unlock() >> >>> >>> Ben. >>> >> >>