On Tue, 19 Oct 2010, Christoph Hellwig wrote: > On Tue, Oct 19, 2010 at 06:00:57PM +1100, Nick Piggin wrote: > > But it is still "magic". Because you don't even know whether it > > is a spin or sleeping lock, let alone whether it is irq or bh safe. > > You get far more information seeing a bit_spin_lock(0, &hlist) call > > than hlist_lock(). Errm, when hlist_lock() has proper documentation than it should not be rocket science to figure out what it does. And if you use bit 0 of hlist then you better have helper functions to access it anyway. We do that with other data types which (ab)use the lower two bits of pointers. > To get back a bit to the point: > > - we have a new bl_hlist sturcture which combines a hash list and a > lock embedded into the head > - the reason why we do it is to be able to use a bitlock And if you design that structure clever, then simple dereferencing of it (w/o casting magic) should make the compiler barf. So you are forced to use the helper functions. > Furthermore it allows the RT people to simply throw a mutex into the > head and everything keeps working without touching a sinlge line of > code outside of hlist_bl.h. Yes, please use proper helper functions. Having to change code is a horror for RT, when we can get away with a single change in a header file. Aside of RT there is another advantage of being able to change the lock implementation at a single place: you can change it to a real spinlock and have lockdep coverage of that code. I fundamentally hate bit_spin_locks for sneaking around lockdep. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
