[Differential] [Changed Subscribers] D1833: Add memory barriers to buf_ring

[andrew (Andrew Turner)]

andrew added a subscriber: andrew.

INLINE COMMENTS
  sys/sys/buf_ring.h:107 atomic_store_rel_int includes a dmb before writing to &br->br_prod_tail.
  
  I don't think this code will be hitting ARM errata 761319 [1] as the read is in a loop where we exit when we see the new value at least once meaning it has been incremented to the value we expect.
  
  . [1] http://infocenter.arm.com/help/topic/com.arm.doc.uan0004a/UAN0004A_a9_read_read.pdf
  sys/sys/buf_ring.h:167 It feels like one or both of these should be read with atomic_load_acq_int.

REVISION DETAIL
  https://reviews.freebsd.org/D1833

To: zbb, kmacy, imp, rpaulo
Cc: andrew, ian, adrian, freebsd-arm