[ovs-git] [openvswitch/ovs] 495c59: pvector: Use acquire-release semantics for size.

[Ilya Maximets]

  Branch: refs/heads/branch-2.8
  Home:   https://github.com/openvswitch/ovs
  Commit: 495c59f14b133f4bd14849897a7194f986154085
      https://github.com/openvswitch/ovs/commit/495c59f14b133f4bd14849897a7194f986154085
  Author: Yanqin Wei <Yanqin.Wei at arm.com>
  Date:   2020-03-13 (Fri, 13 Mar 2020)

  Changed paths:
    M lib/pvector.c
    M lib/pvector.h

  Log Message:
  -----------
  pvector: Use acquire-release semantics for size.

Read/write concurrency of pvector library is implemented by a temp vector
and RCU protection. Considering performance reason, insertion does not
follow this scheme.
In insertion function, a thread fence ensures size increment is done
after new entry is stored. But there is no barrier in the iteration
fuction(pvector_cursor_init). Entry point access may be reordered before
loading vector size, so the invalid entry point may be loaded when vector
iteration.
This patch fixes it by acquire-release pair. It can guarantee new size is
observed by reader after new entry stored by writer. And this is
implemented by one-way barrier instead of two-way memory fence.

Fixes: fe7cfa5c3f19 ("lib/pvector: Non-intrusive RCU priority vector.")
Reviewed-by: Gavin Hu <Gavin.Hu at arm.com>
Reviewed-by: Lijian Zhang <Lijian.Zhang at arm.com>
Signed-off-by: Yanqin Wei <Yanqin.Wei at arm.com>
Signed-off-by: Ilya Maximets <i.maximets at ovn.org>