From: Michael S. Tsirkin Date: Tue, 5 Dec 2017 19:29:37 +0000 (+0200) Subject: ptr_ring: add barriers X-Git-Tag: v4.9.74~46 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=8b032bde28998122bd38cd9e7ee1e52cd15f4773;p=platform%2Fkernel%2Flinux-amlogic.git ptr_ring: add barriers [ 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 Suggested-by: Jason Wang Signed-off-by: Michael S. Tsirkin Acked-by: Jason Wang Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h index b83507c..e38f471 100644 --- a/include/linux/ptr_ring.h +++ b/include/linux/ptr_ring.h @@ -99,12 +99,18 @@ 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; @@ -244,6 +250,9 @@ 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; }