diff options
author | David Laight <David.Laight@ACULAB.COM> | 2023-12-29 23:56:03 +0300 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2023-12-30 21:25:51 +0300 |
commit | 563adbfc351b2af9f1406b809ba60b9f1673a882 (patch) | |
tree | 87fd8337c16d52d018244383e8b679864e443744 /kernel/locking | |
parent | 7c223098212957a1ecd8768e8e747ae2cf88e880 (diff) | |
download | linux-563adbfc351b2af9f1406b809ba60b9f1673a882.tar.xz |
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>
Diffstat (limited to 'kernel/locking')
-rw-r--r-- | kernel/locking/osq_lock.c | 21 |
1 files changed, 9 insertions, 12 deletions
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index d414eef4bec6..15955ce35c53 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -44,26 +44,23 @@ static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val) /* * Get a stable @node->next pointer, either for unlock() or unqueue() purposes. * Can return NULL in case we were the last queued and we updated @lock instead. + * + * If osq_lock() is being cancelled there must be a previous node + * and 'old_cpu' is its CPU #. + * For osq_unlock() there is never a previous node and old_cpu is + * set to OSQ_UNLOCKED_VAL. */ static inline struct optimistic_spin_node * osq_wait_next(struct optimistic_spin_queue *lock, struct optimistic_spin_node *node, - struct optimistic_spin_node *prev) + int old_cpu) { struct optimistic_spin_node *next = NULL; int curr = encode_cpu(smp_processor_id()); - int old; - - /* - * If there is a prev node in queue, then the 'old' value will be - * the prev node's CPU #, else it's set to OSQ_UNLOCKED_VAL since if - * we're currently last in queue, then the queue will then become empty. - */ - old = prev ? prev->cpu : OSQ_UNLOCKED_VAL; for (;;) { if (atomic_read(&lock->tail) == curr && - atomic_cmpxchg_acquire(&lock->tail, curr, old) == curr) { + atomic_cmpxchg_acquire(&lock->tail, curr, old_cpu) == curr) { /* * We were the last queued, we moved @lock back. @prev * will now observe @lock and will complete its @@ -193,7 +190,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) * back to @prev. */ - next = osq_wait_next(lock, node, prev); + next = osq_wait_next(lock, node, prev->cpu); if (!next) return false; @@ -233,7 +230,7 @@ void osq_unlock(struct optimistic_spin_queue *lock) return; } - next = osq_wait_next(lock, node, NULL); + next = osq_wait_next(lock, node, OSQ_UNLOCKED_VAL); if (next) WRITE_ONCE(next->locked, 1); } |