diff options
Diffstat (limited to 'sys/netgraph/ng_base.c')
| -rw-r--r-- | sys/netgraph/ng_base.c | 50 |
1 files changed, 32 insertions, 18 deletions
diff --git a/sys/netgraph/ng_base.c b/sys/netgraph/ng_base.c index cd381e2..7830e12 100644 --- a/sys/netgraph/ng_base.c +++ b/sys/netgraph/ng_base.c @@ -1806,8 +1806,19 @@ static __inline void ng_queue_rw(struct ng_queue * ngq, | Active Writer ---------------------------------------+ - +Node queue has such semantics: +- All flags modifications are atomic. +- Reader count can be incremented only if there is no writer or pending flags. + As soon as this can't be done with single operation, it is implemented with + spin loop and atomic_cmpset(). +- Writer flag can be set only if there is no any bits set. + It is implemented with atomic_cmpset(). +- Pending flag can be set any time, but to avoid collision on queue processing + all queue fields are protected by the mutex. +- Queue processing thread reads queue holding the mutex, but releases it while + processing. When queue is empty pending flag is removed. */ + #define WRITER_ACTIVE 0x00000001 #define OP_PENDING 0x00000002 #define READER_INCREMENT 0x00000004 @@ -1849,19 +1860,16 @@ static __inline void ng_queue_rw(struct ng_queue * ngq, * nothing we could return, either because there really was nothing there, or * because the node was in a state where it cannot yet process the next item * on the queue. - * - * This MUST MUST MUST be called with the mutex held. */ static __inline item_p ng_dequeue(struct ng_queue *ngq, int *rw) { item_p item; + /* This MUST be called with the mutex held. */ mtx_assert(&ngq->q_mtx, MA_OWNED); - /* - * If there is nothing queued, then just return. - * No point in continuing. - */ + + /* If there is nothing queued, then just return. */ if (!QUEUE_ACTIVE(ngq)) { CTR4(KTR_NET, "%20s: node [%x] (%p) queue empty; " "queue flags 0x%lx", __func__, @@ -1878,22 +1886,25 @@ ng_dequeue(struct ng_queue *ngq, int *rw) while (1) { long t = ngq->q_flags; if (t & WRITER_ACTIVE) { - /* It's a reader but we can't use it. */ + /* There is writer, reader can't proceed. */ CTR4(KTR_NET, "%20s: node [%x] (%p) queued reader " "can't proceed; queue flags 0x%lx", __func__, ngq->q_node->nd_ID, ngq->q_node, t); return (NULL); } - if (atomic_cmpset_long(&ngq->q_flags, t, + if (atomic_cmpset_acq_long(&ngq->q_flags, t, t + READER_INCREMENT)) break; cpu_spinwait(); } + /* We have got reader lock for the node. */ *rw = NGQRW_R; - } else if (atomic_cmpset_long(&ngq->q_flags, OP_PENDING, + } else if (atomic_cmpset_acq_long(&ngq->q_flags, OP_PENDING, OP_PENDING + WRITER_ACTIVE)) { + /* We have got writer lock for the node. */ *rw = NGQRW_W; } else { + /* There is somebody other, writer can't proceed. */ CTR4(KTR_NET, "%20s: node [%x] (%p) queued writer " "can't proceed; queue flags 0x%lx", __func__, ngq->q_node->nd_ID, ngq->q_node, ngq->q_flags); @@ -1918,10 +1929,8 @@ ng_dequeue(struct ng_queue *ngq, int *rw) } /* - * Queue a packet to be picked up by someone else. - * We really don't care who, but we can't or don't want to hang around - * to process it ourselves. We are probably an interrupt routine.. - * If the queue could be run, flag the netisr handler to start. + * Queue a packet to be picked up later by someone else. + * If the queue could be run now, add node to the queue handler's worklist. */ static __inline void ng_queue_rw(struct ng_queue * ngq, item_p item, int rw) @@ -1950,6 +1959,7 @@ ng_queue_rw(struct ng_queue * ngq, item_p item, int rw) NG_QUEUE_UNLOCK(ngq); } +/* Acquire reader lock on node. If node is busy, queue the packet. */ static __inline item_p ng_acquire_read(struct ng_queue *ngq, item_p item) { @@ -1961,7 +1971,7 @@ ng_acquire_read(struct ng_queue *ngq, item_p item) long t = ngq->q_flags; if (t & NGQ_RMASK) break; /* Node is not ready for reader. */ - if (atomic_cmpset_long(&ngq->q_flags, t, t + READER_INCREMENT)) { + if (atomic_cmpset_acq_long(&ngq->q_flags, t, t + READER_INCREMENT)) { /* Successfully grabbed node */ CTR4(KTR_NET, "%20s: node [%x] (%p) acquired item %p", __func__, ngq->q_node->nd_ID, ngq->q_node, item); @@ -1976,6 +1986,7 @@ ng_acquire_read(struct ng_queue *ngq, item_p item) return (NULL); } +/* Acquire writer lock on node. If node is busy, queue the packet. */ static __inline item_p ng_acquire_write(struct ng_queue *ngq, item_p item) { @@ -1983,7 +1994,7 @@ ng_acquire_write(struct ng_queue *ngq, item_p item) ("%s: working on deadnode", __func__)); /* Writer needs completely idle node. */ - if (atomic_cmpset_long(&ngq->q_flags, 0, WRITER_ACTIVE)) { + if (atomic_cmpset_acq_long(&ngq->q_flags, 0, WRITER_ACTIVE)) { /* Successfully grabbed node */ CTR4(KTR_NET, "%20s: node [%x] (%p) acquired item %p", __func__, ngq->q_node->nd_ID, ngq->q_node, item); @@ -2070,18 +2081,21 @@ ng_upgrade_write(struct ng_queue *ngq, item_p item) #endif +/* Release reader lock. */ static __inline void ng_leave_read(struct ng_queue *ngq) { - atomic_subtract_long(&ngq->q_flags, READER_INCREMENT); + atomic_subtract_rel_long(&ngq->q_flags, READER_INCREMENT); } +/* Release writer lock. */ static __inline void ng_leave_write(struct ng_queue *ngq) { - atomic_clear_long(&ngq->q_flags, WRITER_ACTIVE); + atomic_clear_rel_long(&ngq->q_flags, WRITER_ACTIVE); } +/* Purge node queue. Called on node shutdown. */ static void ng_flush_input_queue(struct ng_queue * ngq) { |
