lkml.org 
[lkml]   [2014]   [Jan]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: check && lockdep_no_validate (Was: lockdep: Introduce wait-type checks)
On 01/16, Alan Stern wrote:
>
> On Thu, 16 Jan 2014, Peter Zijlstra wrote:
>
> > On Thu, Jan 16, 2014 at 06:43:48PM +0100, Oleg Nesterov wrote:
>
> > > Perhaps we should change the meaning of lockdep_set_novalidate_class?
> > > (perhaps with rename). What do you think about the patch below?
> > >
> > > With this patch __lockdep_no_validate__ means "automatically nested",
> >
> > Yes, I suppose that might work, it would allow some validation.
>
> I haven't seen the patch, but I'm not so sure it will work. Suppose we
> have two devices, D1 and D2, and some other mutex, M. Then the locking
> pattern:
>
> lock(D1);
> lock(M);
> unlock(M);
> unlock(D1);
>
> generally should not conflict with:
>
> lock(M);
> lock(D2);
> unlock(D2);
> unlock(M);

Yes, sure. This change assumes that the only problem in drivers/base is
dev->parent->mutex / dev->mutex dependency. If the locking is even more
"broken" (wrt lockdep), we can't replace lockdep_set_novalidate_class()
with lockdep_set_auto_nested().

And, otoh, with this change lockdep can miss the real problems too, for
example:

func1(dev)
{
device_lock(dev->parent);
mutex_lock(MUTEX);
device_lock(dev);
...
}

func2(dev)
{
device_lock(dev);
mutex_lock(MUTEX);
...
}

lockdep will only notice dev -> MUTEX dependency.

I booted the kernel (under kvm) with this change and there is nothing
in dmesg, but of course this is not the real testing.

So do you think that dev->mutex should not be validated at all ?


Just in case... Of course, if we actually add auto_nested we should not
use a single class unless dev->mutex will be the only user.

Oleg.



\
 
 \ /
  Last update: 2014-01-17 18:21    [W:0.087 / U:6.516 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site