diff options
| author | Michael S. Tsirkin <mst@redhat.com> | 2017-12-05 21:29:37 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-12-11 10:52:23 -0500 |
| commit | a8ceb5dbfde1092b466936bca0ff3be127ecf38e (patch) | |
| tree | 768483ddf27f70faa09ffe0f4a0c90a35119f249 /include | |
| parent | f0f1d0166b17e1fadaa1dfa99721a9abb97e65eb (diff) | |
ptr_ring: add barriers
Users of ptr_ring expect that it's safe to give the
data structure a pointer and have it be available
to consumers, but that actually requires an smb_wmb
or a stronger barrier.
In absence of such barriers and on architectures that reorder writes,
consumer might read an un=initialized value from an skb pointer stored
in the skb array. This was observed causing crashes.
To fix, add memory barriers. The barrier we use is a wmb, the
assumption being that producers do not need to read the value so we do
not need to order these reads.
Reported-by: George Cherian <george.cherian@cavium.com>
Suggested-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/ptr_ring.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h index 37b4bb2545b3..6866df4f31b5 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; @@ -275,6 +281,9 @@ 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; } |