Re: lockdep problem conversion semaphore->mutex (dev->sem)

[Peter Zijlstra]

On Sat, 2007-12-08 at 21:33 +0100, Remy Bohmer wrote:

> Which problems? I did not see any special things, it looked rather
> straight forward. What have I overlooked?

On suspend it locks the whole device tree, this means it has 'unbounded'
nesting and holds an 'unbounded' number of locks. Neither things are
easy to annotate (remember that mutex_lock_nested can handle up to 8
nestings and current->held_locks has a max of 30).

In fact, converting this will be the hardest part, it would require
reworking the locking and introduction of a hard limit on the device
tree depth - this might upset some people, but I suspect that 16 or 24
should be deep enough for pretty much anything. Of course, if people
prove me wrong, I'll have to reconsider. The up-side of the locking
scheme I'm thinking of will be that locking the whole tree will only
take 'depth' number of opterations vs the total number of tree elements.



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