On Wed, Mar 09, 2016 at 11:13:49AM +0100, Peter Zijlstra wrote: > --- > Subject: bitops: Do not default to __clear_bit() for __clear_bit_unlock() > > __clear_bit_unlock() is a special little snowflake. While it carries the > non-atomic '__' prefix, it is specifically documented to pair with > test_and_set_bit() and therefore should be 'somewhat' atomic. > > Therefore the generic implementation of __clear_bit_unlock() cannot use > the fully non-atomic __clear_bit() as a default. > > If an arch is able to do better; is must provide an implementation of > __clear_bit_unlock() itself. > FWIW, we could probably undo this if we unified all the spinlock based atomic ops implementations (there's a whole bunch doing essentially the same), and special cased __clear_bit_unlock() for that. Collapsing them is probably a good idea anyway, just a fair bit of non-trivial work to figure out all the differences and if they matter etc..
