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git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git
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Waiman Long
fb6a44f33b
Without using WRITE_ONCE(), the compiler can potentially break a write into multiple smaller ones (store tearing). So a read from the same data by another task concurrently may return a partial result. This can result in a kernel crash if the data is a memory address that is being dereferenced. This patch changes all write to rwsem->owner to use WRITE_ONCE() to make sure that store tearing will not happen. READ_ONCE() may not be needed for rwsem->owner as long as the value is only used for comparison and not dereferencing. Signed-off-by: Waiman Long <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Dave Chinner <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: Douglas Hatch <[email protected]> Cc: Jason Low <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Peter Hurley <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Scott J Norton <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]>
69 lines
1.9 KiB
C
69 lines
1.9 KiB
C
/*
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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_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 (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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