Messages in this thread Patch in this message |  | | Date | Tue, 4 Feb 2020 10:22:28 +0100 | From | Peter Zijlstra <> | Subject | [PATCH] locking/rwsem: Remove RWSEM_OWNER_UNKNOWN |
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On Tue, Feb 04, 2020 at 09:50:49AM +0100, Peter Zijlstra wrote:
> Anyway, I'll go split, since you seem to care so deeply.
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Subject: locking/rwsem: Remove RWSEM_OWNER_UNKNOWN From: Peter Zijlstra <peterz@infradead.org> Date: Tue Feb 4 09:34:37 CET 2020
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> --- include/linux/rwsem.h | 6 ------ kernel/locking/rwsem.c | 2 -- 2 files changed, 8 deletions(-)
--- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -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) { --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -659,8 +659,6 @@ static inline bool rwsem_can_spin_on_own 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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