locking/percpu-rwsem: Extract __percpu_down_read_trylock()
In preparation for removing the embedded rwsem and building a custom lock, extract the read-trylock primitive. 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/20200131151540.098485539@infradead.org
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@ -45,7 +45,7 @@ void percpu_free_rwsem(struct percpu_rw_semaphore *sem)
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}
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}
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EXPORT_SYMBOL_GPL(percpu_free_rwsem);
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EXPORT_SYMBOL_GPL(percpu_free_rwsem);
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bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
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static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
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{
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{
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__this_cpu_inc(*sem->read_count);
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__this_cpu_inc(*sem->read_count);
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@ -73,11 +73,18 @@ bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
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if (likely(!smp_load_acquire(&sem->readers_block)))
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if (likely(!smp_load_acquire(&sem->readers_block)))
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return true;
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return true;
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/*
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__this_cpu_dec(*sem->read_count);
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* Per the above comment; we still have preemption disabled and
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* will thus decrement on the same CPU as we incremented.
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/* Prod writer to re-evaluate readers_active_check() */
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*/
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rcuwait_wake_up(&sem->writer);
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__percpu_up_read(sem);
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return false;
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}
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bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
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{
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if (__percpu_down_read_trylock(sem))
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return true;
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if (try)
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if (try)
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return false;
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return false;
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