On Tue, Jul 05, 2016 at 02:06:47PM +0300, Jarkko Sakkinen wrote: > This is the basic pattern. Basically we always loose the benefit of > RW-lock because in every use case we also lock a mutex.
The only purpose of the rw lock is protect against unregister, and that is the benifit it provides. > What I was thinking that maybe we could have kref for ops instead > of lock. In the places where we now use read lock you could use > kref_get_unless_zero() to avoid races with tpm_chip_unregister(). No, it needs to be a lock, the unregister path must block and sleep, and a kref cannot do that alone, by the time you build in the locking you've made something more expensive than a rwlock. The performance alternative is to use srcu for the rwlock, but since we don't really have a performance concern in TPM I would rather not see such complexity. Another alternative would be to merge the rw-lock and mutex together (ie hold mutex before touching ops at all), however this semantically changes things by linking the lifetime and concurrancy models together. I belive I looked at that before doing the rwsem and decided it was a huge amount of tricky work. Jason ------------------------------------------------------------------------------ Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San Francisco, CA to explore cutting-edge tech and listen to tech luminaries present their vision of the future. This family event has something for everyone, including kids. Get more information and register today. http://sdm.link/attshape _______________________________________________ tpmdd-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/tpmdd-devel
