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locking/osq_lock: Clarify osq_wait_next() calling convention
osq_wait_next() is passed 'prev' from osq_lock() and NULL from osq_unlock() but only needs the 'cpu' value to write to lock->tail. Just pass prev->cpu or OSQ_UNLOCKED_VAL instead. Should have no effect on the generated code since gcc manages to assume that 'prev != NULL' due to an earlier dereference. Signed-off-by: David Laight <david.laight@aculab.com> [ Changed 'old' to 'old_cpu' by request from Waiman Long - Linus ] Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -44,26 +44,23 @@ static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val)
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/*
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* Get a stable @node->next pointer, either for unlock() or unqueue() purposes.
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* Can return NULL in case we were the last queued and we updated @lock instead.
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*
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* If osq_lock() is being cancelled there must be a previous node
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* and 'old_cpu' is its CPU #.
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* For osq_unlock() there is never a previous node and old_cpu is
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* set to OSQ_UNLOCKED_VAL.
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*/
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static inline struct optimistic_spin_node *
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osq_wait_next(struct optimistic_spin_queue *lock,
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struct optimistic_spin_node *node,
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struct optimistic_spin_node *prev)
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int old_cpu)
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{
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struct optimistic_spin_node *next = NULL;
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int curr = encode_cpu(smp_processor_id());
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int old;
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/*
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* If there is a prev node in queue, then the 'old' value will be
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* the prev node's CPU #, else it's set to OSQ_UNLOCKED_VAL since if
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* we're currently last in queue, then the queue will then become empty.
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*/
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old = prev ? prev->cpu : OSQ_UNLOCKED_VAL;
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for (;;) {
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if (atomic_read(&lock->tail) == curr &&
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atomic_cmpxchg_acquire(&lock->tail, curr, old) == curr) {
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atomic_cmpxchg_acquire(&lock->tail, curr, old_cpu) == curr) {
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/*
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* We were the last queued, we moved @lock back. @prev
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* will now observe @lock and will complete its
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@ -193,7 +190,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
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* back to @prev.
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*/
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next = osq_wait_next(lock, node, prev);
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next = osq_wait_next(lock, node, prev->cpu);
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if (!next)
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return false;
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@ -233,7 +230,7 @@ void osq_unlock(struct optimistic_spin_queue *lock)
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return;
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}
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next = osq_wait_next(lock, node, NULL);
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next = osq_wait_next(lock, node, OSQ_UNLOCKED_VAL);
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if (next)
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WRITE_ONCE(next->locked, 1);
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}
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