Re: [PATCH 00/21] On-demand device registration

Am 12.06.2015 um 09:25 schrieb Linus Walleij:

On Thu, Jun 11, 2015 at 6:40 PM, Alexander Holler [off-list ref] wrote:

quoted

Am 11.06.2015 um 14:30 schrieb Linus Walleij:

quoted

quoted

Certainly it is possible to create deadlocks in this scenario, but the
scope is not to create an ubreakable system.

IAnd what happens if you run into a deadlock? Do you print "you've lost, try
changing your kernel config" in some output hidden by a splash-screen? ;)

Sorry it sounds like a blanket argument, the fact that there are
mutexes in the kernel makes it possible to deadlock, it doesn't
mean we don't use mutexes. Some programming problems are
just like such.

I'm not talking about specific deadlocks through mutexes. I'm talking 
about what happens when driver A needs driver B which needs driver A. 
How do you recognise and handle that with your instrumented on-demand 
device initialization? Such a circular dependency might happen by just 
adding a new fucntion call or by changing the kernel configuration. And 
with the on-demand stuff, the possibility that the developer introducing 
this new (maybe optional) call will never hit such a circular dependency 
is high. So you will end up with a never ending stream of problem 
reports whenever someone introduced such a circular dependecy without 
having noticed it.

And to come back to specific deadlocks, if you are extending function 
calls from something former simple to something which might initialize a 
whole bunch of drivers, needing maybe seconds, I wouldn't say this is a 
blanket argument, but a real thread.

Alexander Holler
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