Re: semantics of reader/writer semaphores in rt patch

2014-10-27 Thread Chris Friesen
On 10/25/2014 04:19 PM, Thomas Gleixner wrote: On Thu, 23 Oct 2014, Chris Friesen wrote: I recently noticed that when CONFIG_PREEMPT_RT_FULL is enabled we the semantics change. From "include/linux/rwsem_rt.h": * Note that the semantics are different from the usual * Linux rw-sems, in PREE

Re: semantics of reader/writer semaphores in rt patch

2014-10-26 Thread Peter Zijlstra
On Sun, Oct 26, 2014 at 08:42:57AM +0100, Peter Zijlstra wrote: > On Sun, Oct 26, 2014 at 12:21:31AM +0200, Thomas Gleixner wrote: > > On Sun, 26 Oct 2014, Thomas Gleixner wrote: > > > On Thu, 23 Oct 2014, Chris Friesen wrote: > > > > Does the RT kernel just disallow this sort of algorithm? > > >

Re: semantics of reader/writer semaphores in rt patch

2014-10-26 Thread Peter Zijlstra
On Sun, Oct 26, 2014 at 12:21:31AM +0200, Thomas Gleixner wrote: > On Sun, 26 Oct 2014, Thomas Gleixner wrote: > > On Thu, 23 Oct 2014, Chris Friesen wrote: > > > Does the RT kernel just disallow this sort of algorithm? > > > > Yes. For a good reason. Let's add thread C > > > > A

Re: semantics of reader/writer semaphores in rt patch

2014-10-25 Thread Thomas Gleixner
On Sun, 26 Oct 2014, Thomas Gleixner wrote: > On Thu, 23 Oct 2014, Chris Friesen wrote: > > Does the RT kernel just disallow this sort of algorithm? > > Yes. For a good reason. Let's add thread C > > A B C > down_read(X) > down_write(X) > lo

Re: semantics of reader/writer semaphores in rt patch

2014-10-25 Thread Thomas Gleixner
On Thu, 23 Oct 2014, Chris Friesen wrote: > I recently noticed that when CONFIG_PREEMPT_RT_FULL is enabled we the > semantics change. From "include/linux/rwsem_rt.h": > > * Note that the semantics are different from the usual > * Linux rw-sems, in PREEMPT_RT mode we do not allow > * multiple

semantics of reader/writer semaphores in rt patch?

2014-10-24 Thread Chris Friesen
I recently noticed that when CONFIG_PREEMPT_RT_FULL is enabled the semantics change. From "include/linux/rwsem_rt.h": * Note that the semantics are different from the usual * Linux rw-sems, in PREEMPT_RT mode we do not allow * multiple readers to hold the lock at once, we only allow * a re