• Robert Jennings's avatar
    powerpc: VPHN topology change updates all siblings · 3be7db6a
    Robert Jennings authored
    When an associativity level change is found for one thread, the
    siblings threads need to be updated as well.  This is done today
    for PRRN in stage_topology_update() but is missing for VPHN in
    update_cpu_associativity_changes_mask().  This patch will correctly
    update all thread siblings during a topology change.
    
    Without this patch a topology update can result in a CPU in
    init_sched_groups_power() getting stuck indefinitely in a loop.
    
    This loop is built in build_sched_groups(). As a result of the thread
    moving to a node separate from its siblings the struct sched_group will
    have its next pointer set to point to itself rather than the sched_group
    struct of the next thread.  This happens because we have a domain without
    the SD_OVERLAP flag, which is correct, and a topology that doesn't conform
    with reality (threads on the same core assigned to different numa nodes).
    When this list is traversed by init_sched_groups_power() it will reach
    the thread's sched_group structure and loop indefinitely; the cpu will
    be stuck at this point.
    
    The bug was exposed when VPHN was enabled in commit b7abef04 (v3.9).
    
    Cc: <stable@vger.kernel.org> [v3.9+]
    Reported-by: default avatarJan Stancek <jstancek@redhat.com>
    Signed-off-by: default avatarRobert Jennings <rcj@linux.vnet.ibm.com>
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    3be7db6a
numa.c 40.6 KB