5149cbac42
For a rwsem, locking can either be exclusive or shared. The corresponding exclusive or shared unlock must be used. Otherwise, the protected data structures may get corrupted or the lock may be in an inconsistent state. In order to detect such anomaly, a new configuration option DEBUG_RWSEMS is added which can be enabled to look for such mismatches and print warnings that that happens. Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1522445280-7767-2-git-send-email-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
75 lines
2.1 KiB
C
75 lines
2.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* The owner field of the rw_semaphore structure will be set to
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* RWSEM_READ_OWNED when a reader grabs the lock. A writer will clear
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* the owner field when it unlocks. A reader, on the other hand, will
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* not touch the owner field when it unlocks.
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*
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* In essence, the owner field now has the following 3 states:
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* 1) 0
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* - lock is free or the owner hasn't set the field yet
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* 2) RWSEM_READER_OWNED
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* - lock is currently or previously owned by readers (lock is free
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* or not set by owner yet)
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* 3) Other non-zero value
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* - a writer owns the lock
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*/
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#define RWSEM_READER_OWNED ((struct task_struct *)1UL)
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#ifdef CONFIG_DEBUG_RWSEMS
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# define DEBUG_RWSEMS_WARN_ON(c) DEBUG_LOCKS_WARN_ON(c)
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#else
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# define DEBUG_RWSEMS_WARN_ON(c)
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#endif
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#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
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/*
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* All writes to owner are protected by WRITE_ONCE() to make sure that
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* store tearing can't happen as optimistic spinners may read and use
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* the owner value concurrently without lock. Read from owner, however,
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* may not need READ_ONCE() as long as the pointer value is only used
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* for comparison and isn't being dereferenced.
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*/
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static inline void rwsem_set_owner(struct rw_semaphore *sem)
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{
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WRITE_ONCE(sem->owner, current);
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}
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static inline void rwsem_clear_owner(struct rw_semaphore *sem)
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{
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WRITE_ONCE(sem->owner, NULL);
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}
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static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
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{
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/*
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* We check the owner value first to make sure that we will only
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* do a write to the rwsem cacheline when it is really necessary
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* to minimize cacheline contention.
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*/
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if (READ_ONCE(sem->owner) != RWSEM_READER_OWNED)
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WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);
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}
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static inline bool rwsem_owner_is_writer(struct task_struct *owner)
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{
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return owner && owner != RWSEM_READER_OWNED;
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}
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static inline bool rwsem_owner_is_reader(struct task_struct *owner)
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{
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return owner == RWSEM_READER_OWNED;
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}
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#else
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static inline void rwsem_set_owner(struct rw_semaphore *sem)
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{
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}
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static inline void rwsem_clear_owner(struct rw_semaphore *sem)
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{
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}
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static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
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{
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}
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#endif
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