On 05/08/09 9:11 -0700, Paul Menage wrote: > On Wed, Aug 5, 2009 at 3:20 AM, Louis Rilling<Louis.Rilling@xxxxxxxxxxx> wrote: > > > > The downside of this is teaching lockdep about this recursive locking. Not that > > simple actually... > > Don't we just give each thread's lock its own lock class? That's what > we did for the cgroup hierarchy_mutex. Given that lock classes must be static and that lockdep only supports a limited lock depth, this is an issue for processes having many threads. > > > so that such cases are currently handled using a higher-level > > lock that prevents races in locking the whole chain (there was one such example > > for locking all vmas with KVM). IIUC, the intent here is to avoid such > > higher-level lock. > > cgroup_mutex already fulfills the role of the higher-level lock. If so (that is, here cgroup_mutex is taken before write-locking all threads' rw_sem), then enhancing rwsem's interface in a similar way to the spin_lock_nest_lock() interface could do it. There will still be an issue with many threads and lockdep limited lock depth though. Added Peter in CC. Louis -- Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes
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