Re: check && lockdep_no_validate (Was: lockdep: Introducewait-type checks)
From: Oleg Nesterov
Date: Fri Jan 17 2014 - 11:31:31 EST
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
> generally should not conflict with:
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()
And, otoh, with this change lockdep can miss the real problems too, for
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.
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