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Date: Sun, 28 Apr 2019 11:57:51 -0400 From: Waiman Long <longman@...hat.com> To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com> Cc: linux-kernel@...r.kernel.org, x86@...nel.org, Davidlohr Bueso <dave@...olabs.net>, Linus Torvalds <torvalds@...ux-foundation.org>, Tim Chen <tim.c.chen@...ux.intel.com>, huang ying <huang.ying.caritas@...il.com>, Waiman Long <longman@...hat.com> Subject: [PATCH-tip v6 16/20] locking/rwsem: Add more rwsem owner access helpers Before combining owner and count, we are adding two new helpers for accessing the owner value in the rwsem. 1) struct task_struct *rwsem_get_owner(struct rw_semaphore *sem) 2) bool is_rwsem_reader_owned(struct rw_semaphore *sem) Signed-off-by: Waiman Long <longman@...hat.com> --- kernel/locking/rwsem.c | 41 ++++++++++++++++++++++++++++++----------- 1 file changed, 30 insertions(+), 11 deletions(-) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 04156b62d1d7..eadd375c89a3 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -165,6 +165,11 @@ static inline void rwsem_clear_owner(struct rw_semaphore *sem) WRITE_ONCE(sem->owner, NULL); } +static inline struct task_struct *rwsem_get_owner(struct rw_semaphore *sem) +{ + return READ_ONCE(sem->owner); +} + /* * The task_struct pointer of the last owning reader will be left in * the owner field. @@ -218,6 +223,23 @@ static inline struct task_struct *owner_without_flags(struct task_struct *owner) return (struct task_struct *)((long)owner & ~RWSEM_OWNER_FLAGS_MASK); } +/* + * Return true if the rwsem is owned by a reader. + */ +static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem) +{ +#ifdef CONFIG_DEBUG_RWSEMS + /* + * Check the count to see if it is write-locked. + */ + long count = atomic_long_read(&sem->count); + + if (count & RWSEM_WRITER_MASK) + return false; +#endif + return (unsigned long)sem->owner & RWSEM_READER_OWNED; +} + #ifdef CONFIG_DEBUG_RWSEMS /* * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there @@ -230,7 +252,7 @@ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem) unsigned long owner = (unsigned long)READ_ONCE(sem->owner); if ((owner & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) - cmpxchg_relaxed((unsigned long *)&sem->owner, val, + cmpxchg_relaxed((unsigned long *)&sem->owner, owner, owner & RWSEM_OWNER_FLAGS_MASK); } #else @@ -613,7 +635,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem, bool wr) preempt_disable(); rcu_read_lock(); - owner = READ_ONCE(sem->owner); + owner = rwsem_get_owner(sem); if (!is_rwsem_owner_spinnable(owner, wr)) ret = false; else if ((unsigned long)owner & RWSEM_READER_OWNED) @@ -663,7 +685,7 @@ static inline enum owner_state rwsem_owner_state(unsigned long owner, bool wr) static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem, bool wr) { - struct task_struct *tmp, *owner = READ_ONCE(sem->owner); + struct task_struct *tmp, *owner = rwsem_get_owner(sem); enum owner_state state = rwsem_owner_state((unsigned long)owner, wr); if (state != OWNER_WRITER) @@ -676,7 +698,7 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, bool wr) break; } - tmp = READ_ONCE(sem->owner); + tmp = rwsem_get_owner(sem); if (tmp != owner) { state = rwsem_owner_state((unsigned long)tmp, wr); break; @@ -1275,8 +1297,7 @@ inline void __down_read(struct rw_semaphore *sem) if (unlikely(atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count) & RWSEM_READ_FAILED_MASK)) { rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE); - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & - RWSEM_READER_OWNED), sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } else { rwsem_set_reader_owned(sem); } @@ -1288,8 +1309,7 @@ static inline int __down_read_killable(struct rw_semaphore *sem) &sem->count) & RWSEM_READ_FAILED_MASK)) { if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE))) return -EINTR; - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & - RWSEM_READER_OWNED), sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } else { rwsem_set_reader_owned(sem); } @@ -1360,7 +1380,7 @@ inline void __up_read(struct rw_semaphore *sem) { long tmp; - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED), sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); rwsem_clear_reader_owned(sem); tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count); if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) == @@ -1574,8 +1594,7 @@ EXPORT_SYMBOL(down_write_killable_nested); void up_read_non_owner(struct rw_semaphore *sem) { - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED), - sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); __up_read(sem); } EXPORT_SYMBOL(up_read_non_owner); -- 2.18.1
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