On Wed, Mar 25, 2020 at 05:02:12PM +0100, Sebastian Siewior wrote: > On 2020-03-25 13:27:49 [+0100], Thomas Gleixner wrote: > > The documentation of rw_semaphores is wrong as it claims that the non-owner > > reader release is not supported by RT. That's just history biased memory > > distortion. > > > > Split the 'Owner semantics' section up and add separate sections for > > semaphore and rw_semaphore to reflect reality. > > > > Aside of that the following updates are done: > > > > - Add pseudo code to document the spinlock state preserving mechanism on > > PREEMPT_RT > > > > - Wordsmith the bitspinlock and lock nesting sections > > > > Co-developed-by: Paul McKenney <paulmck@xxxxxxxxxx> > > Signed-off-by: Paul McKenney <paulmck@xxxxxxxxxx> > > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Acked-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > > > --- a/Documentation/locking/locktypes.rst > > +++ b/Documentation/locking/locktypes.rst > … > > +rw_semaphore > > +============ > > + > > +rw_semaphore is a multiple readers and single writer lock mechanism. > > + > > +On non-PREEMPT_RT kernels the implementation is fair, thus preventing > > +writer starvation. > > + > > +rw_semaphore complies by default with the strict owner semantics, but there > > +exist special-purpose interfaces that allow non-owner release for readers. > > +These work independent of the kernel configuration. > > This reads funny, could be my English. "This works independent …" maybe? The "These" refers to "interfaces", which is plural, so "These" rather than "This". But yes, it is a bit awkward, because you have to skip back past "readers", "release", and "non-owner" to find the implied subject of that last sentence. So how about this instead, making the implied subject explicit? rw_semaphore complies by default with the strict owner semantics, but there exist special-purpose interfaces that allow non-owner release for readers. These interfaces work independent of the kernel configuration. Thanx, Paul
