On Tuesday 08 December 2009, Linus Torvalds wrote: > > On Tue, 8 Dec 2009, Rafael J. Wysocki wrote: > > > > The wait queue plus the op_complete flag combo plays the role of the locking > > in the Linus' picture > > Please just use the lock. Don't make up your own locking crap. Really. > > Your patch is horrible. Exactly because your locking is horribly > mis-designed. You can't say things are complete from an interrupt, for > example, since you made it some random bitfield, which has unknown > characteristics (ie non-atomic read-modify-write etc). I didn't assume anyone would check it from an interrupt, because I didn't see a point. In fact I didn't assume anyone except for the PM core would check it. In case this assumption is wrong, it can be easily put under the dev->sem that we take anyway before calling the bus type (etc.) callbacks. Anyway, if we use an rwsem, it won't be checkable from interrupt context just as well. > The fact is, any time anybody makes up a new locking mechanism, THEY > ALWAYS GET IT WRONG. Don't do it. > > I suggested using the rwsem locking for a good reason. It made sense. It > was simpler. Just do it that way, stop making up crap. Suppose we use rwsem and during suspend each child uses a down_read() on a parent and then the parent uses down_write() on itself. What if, whatever the reason, the parent is a bit early and does the down_write() before one of the children has a chance to do the down_read()? Aren't we toast? Do we need any direct protection against that or does it just work itself out in a way I just don't see right now? Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
