1. 20 Dec, 2011 1 commit
    • David Rientjes's avatar
      cpusets: stall when updating mems_allowed for mempolicy or disjoint nodemask · b246272e
      David Rientjes authored
      Kernels where MAX_NUMNODES > BITS_PER_LONG may temporarily see an empty
      nodemask in a tsk's mempolicy if its previous nodemask is remapped onto a
      new set of allowed cpuset nodes where the two nodemasks, as a result of
      the remap, are now disjoint.
      
      c0ff7453 ("cpuset,mm: fix no node to alloc memory when changing
      cpuset's mems") adds get_mems_allowed() to prevent the set of allowed
      nodes from changing for a thread.  This causes any update to a set of
      allowed nodes to stall until put_mems_allowed() is called.
      
      This stall is unncessary, however, if at least one node remains unchanged
      in the update to the set of allowed nodes.  This was addressed by
      89e8a244 ("cpusets: avoid looping when storing to mems_allowed if one
      node remains set"), but it's still possible that an empty nodemask may be
      read from a mempolicy because the old nodemask may be remapped to the new
      nodemask during rebind.  To prevent this, only avoid the stall if there is
      no mempolicy for the thread being changed.
      
      This is a temporary solution until all reads from mempolicy nodemasks can
      be guaranteed to not be empty without the get_mems_allowed()
      synchronization.
      
      Also moves the check for nodemask intersection inside task_lock() so that
      tsk->mems_allowed cannot change.  This ensures that nothing can set this
      tsk's mems_allowed out from under us and also protects tsk->mempolicy.
      Reported-by: default avatarMiao Xie <miaox@cn.fujitsu.com>
      Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
      Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Paul Menage <paul@paulmenage.org>
      Cc: Stephen Rothwell <sfr@canb.auug.org.au>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      b246272e
  2. 19 Dec, 2011 6 commits
  3. 18 Dec, 2011 7 commits
  4. 17 Dec, 2011 3 commits
  5. 16 Dec, 2011 23 commits