On 03/09/2015 12:29 PM, Mike Galbraith wrote: > On Mon, 2015-03-09 at 12:07 +0100, Sebastian Andrzej Siewior wrote: >> On 03/09/2015 11:51 AM, Mike Galbraith wrote: >>> Why do both mutex and rtmutex then exist one might ask? ;-) No big deal >>> either way though, it's not like it becomes immutable once applied. >> >> You don't choose rtmutex afaik. rtmutex is used by futex (only?) > > Almost only, but not quite. > > drivers/media/usb/em28xx/em28xx.h: struct rt_mutex i2c_bus_lock; > include/linux/i2c.h: struct rt_mutex bus_lock; > kernel/rcu/tree.h: struct rt_mutex boost_mtx;
So you have two users here: RCU and i2c-bus. The RCU thingy came from -RT (I think). and I2C is actually one user. I am not sure Mauro used the rt-mutex in em28xx for a reason or just blindly copied the i2c code. The i2c-core holds a bus_lock so I don't think he needs to do the same thing. And i2c is the other user. It does a try_lock() in "irq_disabled()" context which records the wrong owner for PI-boosting if it is used from IRQ context. I'm not against it but from ww-mutex point it makes most likely sense to switch them all and not decide which one to switch. Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
