| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 31/75] ptr_ring: add barriers | Date | Mon, 1 Jan 2018 15:32:08 +0100 |
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4.9-stable review patch. If anyone has any objections, please let me know.
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From: "Michael S. Tsirkin" <mst@redhat.com>
[ Upstream commit a8ceb5dbfde1092b466936bca0ff3be127ecf38e ]
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- include/linux/ptr_ring.h | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/include/linux/ptr_ring.h +++ b/include/linux/ptr_ring.h @@ -99,12 +99,18 @@ static inline bool ptr_ring_full_bh(stru /* 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; @@ -244,6 +250,9 @@ static inline void *__ptr_ring_consume(s 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; }
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