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    SubjectRe: latest -git: WARNING: at arch/x86/kernel/ipi.c:123 send_IPI_mask_bitmask+0xc3/0xe0()
    On Wed, Aug 20, 2008 at 08:26:19AM +0200, Vegard Nossum wrote:
    > On Wed, Aug 20, 2008 at 3:39 AM, Andi Kleen <> wrote:
    > > On Tue, Aug 19, 2008 at 09:51:44PM +0200, Vegard Nossum wrote:
    > >> Hi,
    > >>
    > >> With latest -git (1fca25427482387689fa27594c992a961d98768f), I got
    > >> this on reading from /dev/cpu/*/* while hot-unplugging cpu1.
    > >
    > > It's generally known the oprofile doesn't support CPU hotplug well.
    > > Someone needs to make a project out of fixing it properly. Right now
    > > it's just a "don't do that when it hurts"
    > Hm. What you say is true, but this one in particular has nothing to do
    > with oprofile! It has something to do with reading /dev/cpu/*/msr
    > while hot-unplugging cpu1:
    > [<c011733e>] msr_read+0x6e/0xa0
    > [<c01a87b4>] vfs_read+0x94/0x130
    > I wasn't using oprofile when this happened. So I think it should also
    > be considered a separate issue. Though yes -- CPU hotplug in general
    > tends to break a lot of things.

    From my reading of the msr code, we check that the cpu is online in ->open,
    but we never check it again, and also, we make no guarantees that it
    won't go away before we ->read or even ->close it.

    Would adding a get_cpu/put_cpu across the open/close solve this?



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