[PATCH] ptr_ring: add barriers
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2017-12-05 19:29:43
Also in:
lkml, virtualization
Subsystem:
the rest · Maintainer:
Linus Torvalds
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 <redacted> Suggested-by: Jason Wang <redacted> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- George, could you pls report whether this patch fixes the issue for you? This seems to be needed in stable as well. include/linux/ptr_ring.h | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 37b4bb2..6866df4 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; }
--
MST