Ocfs2 devel - Dec 2015 - [PATCH] ocfs2: dlm: fix recursive locking deadlock

On Mon, Dec 14, 2015 at 02:03:17PM +0800, Junxiao Bi
wrote:
> > Second, this issue can be reproduced in old Linux kernels (e.g.
3.16.7-24)? there should not be any regression issue?
> Maybe just hard to reproduce, ocfs2 supports recursive locking.
In what sense? The DLM might but the FS should never be making use of such a
mechanism (it would be for userspace users).

We really can't add recursive locks without this getting rejected upstream.
There's a whole slew of reasons why we don't like those in the kernel.
	--Mark

--
Mark Fasheh

Hi Mark,

On 12/15/2015 03:18 AM, Mark Fasheh wrote:
> On Mon, Dec 14, 2015 at 02:03:17PM +0800, Junxiao Bi wrote:
>>> Second, this issue can be reproduced in old Linux kernels (e.g.
3.16.7-24)? there should not be any regression issue?
>> Maybe just hard to reproduce, ocfs2 supports recursive locking.
> 
> In what sense? The DLM might but the FS should never be making use of such
a
> mechanism (it would be for userspace users).
See commit 743b5f1434f5 ("ocfs2: take inode lock in
ocfs2_iop_set/get_acl()"), it used recursive locking and caused a
deadlock, the call trace is in this patch's log.
> 
> We really can't add recursive locks without this getting rejected
upstream.
> There's a whole slew of reasons why we don't like those in the
kernel.
Is there any harm to support this lock in kernel?

Thanks,
Junxiao.
> 	--Mark
> 
> --
> Mark Fasheh
>