Re: [dm-devel] [PATCH] dm: Fix lock dependency warning for request based dm

[Christof Schmitt <christof schmitt de ibm com>]

On Thu, Feb 19, 2009 at 12:02:23PM +0900, Kiyoshi Ueda wrote:
> Hi Christof,
> 
> On 2009/02/18 23:21 +0900, Christof Schmitt wrote:
> > > From: Christof Schmitt <christof schmitt de ibm com>
> > > 
> > > Testing with request based dm multipathing and lock dependency checking
> > > revealed this problem. Fix this by disabling interrupts when acquiring the
> > > map_lock from the ioctl call in __bind and __unbind.
> > > 
> > > It seems that the problem has been introduced with this patch:
> > > http://lkml.indiana.edu/hypermail/linux/kernel/0810.0/1067.html
> 
> Thank you for your testing request-based dm-multipath and the patch.
> 
> Attached is a patch to fix it.
> Since request-based dm gets map_lock after taking queue_lock with
> interrupt disabled, we have to use save/restore variant.
> (By the way, although lockdep warns the deadlock possibility, currently
>  there should be no such code path in request-based dm where request_fn
>  is called from the interrupt context.)

I was checking for other locking problems when this warning from
lockdep showed up. While i agree that it is only a problem in theory,
it deserves fixing to continue using lockdep.

> I have done simple build and boot testings, but haven't done other
> testings (e.g. stress testing) yet.
> I will include this patch to the next update after such testings.

Thanks for the updated patch. I will include this one in future tests.

--
Christof Schmitt