1. 27 Apr, 2014 1 commit
    • Mikulas Patocka's avatar
      user namespace: fix incorrect memory barriers · 98afe6df
      Mikulas Patocka authored
      commit e79323bd upstream.
      
      smp_read_barrier_depends() can be used if there is data dependency between
      the readers - i.e. if the read operation after the barrier uses address
      that was obtained from the read operation before the barrier.
      
      In this file, there is only control dependency, no data dependecy, so the
      use of smp_read_barrier_depends() is incorrect. The code could fail in the
      following way:
      * the cpu predicts that idx < entries is true and starts executing the
        body of the for loop
      * the cpu fetches map->extent[0].first and map->extent[0].count
      * the cpu fetches map->nr_extents
      * the cpu verifies that idx < extents is true, so it commits the
        instructions in the body of the for loop
      
      The problem is that in this scenario, the cpu read map->extent[0].first
      and map->nr_extents in the wrong order. We need a full read memory barrier
      to prevent it.
      Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      98afe6df
  2. 14 Apr, 2014 39 commits