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@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.