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.c...@huawei.com> > > > > > > > > > > > > > > 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? > 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. -- Ben Hutchings Software Developer, Codethink Ltd.
