Messages in this thread | | | Date | Thu, 15 Jul 2021 11:27:03 +0200 | From | Peter Zijlstra <> | Subject | Re: [patch 03/50] sched: Prepare for RT sleeping spin/rwlocks |
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On Thu, Jul 15, 2021 at 12:20:28AM +0100, Valentin Schneider wrote: > Hi, > > On 13/07/21 17:10, Thomas Gleixner wrote: > > From: Thomas Gleixner <tglx@linutronix.de> > > > > Waiting for spinlocks and rwlocks on non RT enabled kernels is task::state > > preserving. Any wakeup which matches the state is valid. > > > > RT enabled kernels substitutes them with 'sleeping' spinlocks. This creates > > an issue vs. task::state. > > > > In order to block on the lock the task has to overwrite task::state and a > > consecutive wakeup issued by the unlocker sets the state back to > > TASK_RUNNING. As a consequence the task loses the state which was set > > before the lock acquire and also any regular wakeup targeted at the task > > while it is blocked on the lock. > > > > I'm not sure I get this for spinlocks - p->__state != TASK_RUNNING means > task is stopped (or about to be), IMO that doesn't go with spinning. I was > thinking perhaps ptrace could be an issue, but I don't have a clear picture > on that either. What am I missing?
spinlocks will become rtmutex. They're going to clobber __state by virtue of a nested block.
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