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    SubjectRe: [Bugfix] sched: fix possible invalid memory access caused by CPU hot-addition


    On 2014/4/23 9:59, David Rientjes wrote:
    > On Tue, 22 Apr 2014, Peter Zijlstra wrote:
    >
    >> On Tue, Apr 22, 2014 at 01:01:51PM -0700, Andrew Morton wrote:
    >>> On Tue, 22 Apr 2014 10:15:15 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
    >>>
    >>>> On Tue, Apr 22, 2014 at 01:27:15PM +0800, Jiang Liu wrote:
    >>>>> When calling kzalloc_node(size, flags, node), we should first check
    >>>>> whether node is onlined, otherwise it may cause invalid memory access
    >>>>> as below.
    >>>>
    >>>> But this is only for memory less node crap, right?
    >>>
    >>> um, why are memoryless nodes crap?
    >>
    >> Why wouldn't they be? Having CPUs with no local memory seems decidedly
    >> suboptimal.
    >
    > The quick fix for memoryless node issues is usually just do cpu_to_mem()
    > rather than cpu_to_node() in the caller. This assumes that the arch is
    > setup correctly to handle memoryless nodes with
    > CONFIG_HAVE_MEMORYLESS_NODES (and we've had problems recently with
    > memoryless nodes not being configured correctly on powerpc).
    >
    > That type of a fix would probably be better handled in the slab allocator,
    > though, since kmalloc_node(nid) shouldn't crash just because nid is
    > memoryless, we should be doing local_memory_node(node) when allocating the
    > slab pages.
    >
    > However, I don't think memoryless nodes are the problem here since Jiang
    > is testing for !node_online(nid) in his patch, so it's a problem with
    > cpu_to_node() pointing to an offline node. It makes sense for the page
    > allocator to crash in such a case, the node id is erroneous.
    >
    > So either the cpu-to-node mapping is invalid or alloc_fair_sched_group()
    > is allocating memory for a cpu on an offline node. The
    > for_each_possible_cpu() looks suspicious. There's no guarantee that
    > local_memory_node(node) for an offline node will return anything with
    > affinity, so falling back to NUMA_NO_NODE looks appropriate in Jiang's
    > patch.
    Hi David,
    That's the case, alloc_fair_sched_group() is trying to allocate
    memory for CPU in offline node, which then access non-exist NODE_DATA.
    Thanks!
    Gerry

    >


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