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    SubjectRe: [RFC PATCH 00/19] Foundation for automatic NUMA balancing
    On Wed, Nov 07, 2012 at 05:27:12PM +0800, Zhouping Liu wrote:
    >
    > Hello Mel,
    >
    > my 2 nodes machine hit a panic fault after applied the patch
    > set(based on kernel-3.7.0-rc4), please review it:
    >
    > <SNIP>

    Early initialisation problem by the looks of things. Try this please

    ---8<---
    mm: numa: Check that preferred_node_policy is initialised

    Zhouping Liu reported the following

    [ 0.000000] ------------[ cut here ]------------
    [ 0.000000] kernel BUG at mm/mempolicy.c:1785!
    [ 0.000000] invalid opcode: 0000 [#1] SMP
    [ 0.000000] Modules linked in:
    [ 0.000000] CPU 0
    ....
    [ 0.000000] Call Trace:
    [ 0.000000] [<ffffffff81176966>] alloc_pages_current+0xa6/0x170
    [ 0.000000] [<ffffffff81137a44>] __get_free_pages+0x14/0x50
    [ 0.000000] [<ffffffff819efd9b>] kmem_cache_init+0x53/0x2d2
    [ 0.000000] [<ffffffff819caa53>] start_kernel+0x1e0/0x3c7

    Problem is that early in boot preferred_nod_policy and SLUB
    initialisation trips up. Check it is initialised.

    Signed-off-by: Mel Gorman <mgorman@suse.de>
    ---
    mm/mempolicy.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/mm/mempolicy.c b/mm/mempolicy.c
    index 11d4b6b..8cfa6dc 100644
    --- a/mm/mempolicy.c
    +++ b/mm/mempolicy.c
    @@ -129,6 +129,10 @@ static struct mempolicy *get_task_policy(struct task_struct *p)
    node = numa_node_id();
    if (node != -1)
    pol = &preferred_node_policy[node];
    +
    + /* preferred_node_policy is not initialised early in boot */
    + if (!pol->mode)
    + pol = NULL;
    }

    return pol;

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