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| author | Yanfei Xu <yanfei.xu@windriver.com> | 2021-10-13 21:41:52 +0800 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-10-19 17:27:06 +0200 |
| commit | 6c2787f2a20ceb49c98bd06f7dad1589eed1c951 (patch) | |
| tree | 087af925e2290780f932b1b960ae47beb1db663f /kernel/locking/rwsem.c | |
| parent | 7cdacc5f52d68a9370f182c844b5b3e6cc975cc1 (diff) | |
| download | linux-next-6c2787f2a20ceb49c98bd06f7dad1589eed1c951.tar.gz | |
locking: Remove rcu_read_{,un}lock() for preempt_{dis,en}able()
preempt_disable/enable() is equal to RCU read-side crital section, and
the spinning codes in mutex and rwsem could ensure that the preemption
is disabled. So let's remove the unnecessary rcu_read_lock/unlock for
saving some cycles in hot codes.
Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20211013134154.1085649-2-yanfei.xu@windriver.com
Diffstat (limited to 'kernel/locking/rwsem.c')
| -rw-r--r-- | kernel/locking/rwsem.c | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 29eea50a3e67..884aa08e0624 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -635,7 +635,10 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) } preempt_disable(); - rcu_read_lock(); + /* + * Disable preemption is equal to the RCU read-side crital section, + * thus the task_strcut structure won't go away. + */ owner = rwsem_owner_flags(sem, &flags); /* * Don't check the read-owner as the entry may be stale. @@ -643,7 +646,6 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) if ((flags & RWSEM_NONSPINNABLE) || (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner))) ret = false; - rcu_read_unlock(); preempt_enable(); lockevent_cond_inc(rwsem_opt_fail, !ret); @@ -671,12 +673,13 @@ rwsem_spin_on_owner(struct rw_semaphore *sem) unsigned long flags, new_flags; enum owner_state state; + lockdep_assert_preemption_disabled(); + owner = rwsem_owner_flags(sem, &flags); state = rwsem_owner_state(owner, flags); if (state != OWNER_WRITER) return state; - rcu_read_lock(); for (;;) { /* * When a waiting writer set the handoff flag, it may spin @@ -694,7 +697,9 @@ rwsem_spin_on_owner(struct rw_semaphore *sem) * Ensure we emit the owner->on_cpu, dereference _after_ * checking sem->owner still matches owner, if that fails, * owner might point to free()d memory, if it still matches, - * the rcu_read_lock() ensures the memory stays valid. + * our spinning context already disabled preemption which is + * equal to RCU read-side crital section ensures the memory + * stays valid. */ barrier(); @@ -705,7 +710,6 @@ rwsem_spin_on_owner(struct rw_semaphore *sem) cpu_relax(); } - rcu_read_unlock(); return state; } |