On Mon, Mar 09, 2015 at 02:21:53PM +0100, Sebastian Andrzej Siewior wrote: > 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).
RCU uses rt_mutex rather than mutex because it needs rt_mutex's priority-inheritance features for RCU priority boosting. This did indeed originally come from -rt, but is now in mainline. If mutex gains rt_mutex's priority-boosting capability, then RCU could switch to mutex. But you both probably knew all that already... Thanx, Paul > 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 majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/