diff options
| author | Andrew Turner <andrew@FreeBSD.org> | 2024-08-19 09:06:52 +0000 |
|---|---|---|
| committer | Andrew Turner <andrew@FreeBSD.org> | 2024-09-02 08:49:38 +0000 |
| commit | 80df53c7fb1cefffff419adbb0767f36a44c27d2 (patch) | |
| tree | c4e9a36d2cba3ab70071d7e755847d2f58de3dd3 | |
| parent | 56e8c3ec5241ec4747b8fdd42e0172325c7fc378 (diff) | |
buf_ring: Use atomic operations with br_cons_tail
Use an atomic operation with a memory barrier loading br_cons_tail
from the producer thread and storing to it in the consumer thread.
On dequeue we need to read the pointer value from the buf_ring before
moving the consumer tail as that indicates the entry is available to be
used. The store release atomic operation guarantees this.
In the enqueueing thread we then need to use a load acquire atomic
operation to ensure writing to this entry can only happen after the
tail has been read and checked.
Reported by: Ali Saidi <alisaidi@amazon.com>
Co-developed by: Ali Saidi <alisaidi@amazon.com>
Reviewed by: markj
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D46152
(cherry picked from commit 44e1cfca417c5ef0db908f3836ec3ba704ef1de2)
| -rw-r--r-- | sys/sys/buf_ring.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/sys/sys/buf_ring.h b/sys/sys/buf_ring.h index dec0f971ae44..9aeb5aa19fa8 100644 --- a/sys/sys/buf_ring.h +++ b/sys/sys/buf_ring.h @@ -91,7 +91,7 @@ buf_ring_enqueue(struct buf_ring *br, void *buf) do { prod_head = br->br_prod_head; prod_next = prod_head + 1; - cons_tail = br->br_cons_tail; + cons_tail = atomic_load_acq_32(&br->br_cons_tail); if ((int32_t)(cons_tail + br->br_prod_size - prod_next) < 1) { rmb(); @@ -229,7 +229,7 @@ buf_ring_dequeue_sc(struct buf_ring *br) panic("inconsistent list cons_tail=%d cons_head=%d", br->br_cons_tail, cons_head); #endif - br->br_cons_tail = cons_next; + atomic_store_rel_32(&br->br_cons_tail, cons_next); return (buf); } @@ -257,7 +257,7 @@ buf_ring_advance_sc(struct buf_ring *br) #ifdef DEBUG_BUFRING br->br_ring[cons_head & mask] = NULL; #endif - br->br_cons_tail = cons_next; + atomic_store_rel_32(&br->br_cons_tail, cons_next); } /* |