diff options
Diffstat (limited to 'include/linux/ptr_ring.h')
| -rw-r--r-- | include/linux/ptr_ring.h | 23 |
1 files changed, 19 insertions, 4 deletions
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h index 37b4bb2545b3..d72b2e7dd500 100644 --- a/include/linux/ptr_ring.h +++ b/include/linux/ptr_ring.h @@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r) /* Note: callers invoking this in a loop must use a compiler barrier, * for example cpu_relax(). Callers must hold producer_lock. + * Callers are responsible for making sure pointer that is being queued + * points to a valid data. */ static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr) { if (unlikely(!r->size) || r->queue[r->producer]) return -ENOSPC; + /* Make sure the pointer we are storing points to a valid data. */ + /* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */ + smp_wmb(); + r->queue[r->producer++] = ptr; if (unlikely(r->producer >= r->size)) r->producer = 0; @@ -168,6 +174,15 @@ static inline int ptr_ring_produce_bh(struct ptr_ring *r, void *ptr) * if they dereference the pointer - see e.g. PTR_RING_PEEK_CALL. * If ring is never resized, and if the pointer is merely * tested, there's no need to take the lock - see e.g. __ptr_ring_empty. + * However, if called outside the lock, and if some other CPU + * consumes ring entries at the same time, the value returned + * is not guaranteed to be correct. + * In this case - to avoid incorrectly detecting the ring + * as empty - the CPU consuming the ring entries is responsible + * for either consuming all ring entries until the ring is empty, + * or synchronizing with some other CPU and causing it to + * execute __ptr_ring_peek and/or consume the ring enteries + * after the synchronization point. */ static inline void *__ptr_ring_peek(struct ptr_ring *r) { @@ -176,10 +191,7 @@ static inline void *__ptr_ring_peek(struct ptr_ring *r) return NULL; } -/* Note: callers invoking this in a loop must use a compiler barrier, - * for example cpu_relax(). Callers must take consumer_lock - * if the ring is ever resized - see e.g. ptr_ring_empty. - */ +/* See __ptr_ring_peek above for locking rules. */ static inline bool __ptr_ring_empty(struct ptr_ring *r) { return !__ptr_ring_peek(r); @@ -275,6 +287,9 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r) if (ptr) __ptr_ring_discard_one(r); + /* Make sure anyone accessing data through the pointer is up to date. */ + /* Pairs with smp_wmb in __ptr_ring_produce. */ + smp_read_barrier_depends(); return ptr; } |