Commit bcba67cd authored Feb 04, 2020 by Peter Zijlstra Committed by Ingo Molnar Feb 11, 2020

locking/rwsem: Remove RWSEM_OWNER_UNKNOWN



Remove the now unused RWSEM_OWNER_UNKNOWN hack. This hack breaks
PREEMPT_RT and getting rid of it was the entire motivation for
re-writing the percpu rwsem.

The biggest problem is that it is fundamentally incompatible with any
form of Priority Inheritance, any exclusively held lock must have a
distinct owner.

Requested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200204092228.GP14946@hirez.programming.kicks-ass.net

parent 7f26482a

include/linux/rwsem.h

+0 −6

Original line number	Diff line number	Diff line
		@@ -53,12 +53,6 @@ struct rw_semaphore {
		#endif
		};

		/*
		* Setting all bits of the owner field except bit 0 will indicate
		* that the rwsem is writer-owned with an unknown owner.
		*/
		#define RWSEM_OWNER_UNKNOWN (-2L)

		/* In all implementations count != 0 means locked */
		static inline int rwsem_is_locked(struct rw_semaphore *sem)
		{

kernel/locking/rwsem.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -659,8 +659,6 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
		unsigned long flags;
		bool ret = true;

		BUILD_BUG_ON(!(RWSEM_OWNER_UNKNOWN & RWSEM_NONSPINNABLE));

		if (need_resched()) {
		lockevent_inc(rwsem_opt_fail);
		return false;

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