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    SubjectRe: [PATCH] kdump: Enable kdump if 2nd-kernel is loaded.

    Hi Seto-san,

    Thank you for your comment.

    Hidetoshi Seto wrote:
    >> This patch enables a kdump if 2nd-kernel is loaded.
    >> (The patch is based on linux-2.6.31-rc2.)
    >>
    >> Now, a kdump is enabled if a kernel parameter "oops=panic" is specified and
    >> 2nd-kernel is loaded. I think that a kdump should be enabled regardless of
    >> "oops=panic" if 2nd-kernel is loaded, because a system administrator loads
    >> 2nd-kernel for enabling a kdump.
    >
    > I think this description is slightly wrong because kdump will be invoked
    > from panic, regardless of the panic_on_oops.
    >
    > Maybe:
    > A kdump on oops is enabled if a kernel parameter "oops=panic" ...
    > ~~~~~~~

    Right, I should add "on oops" to the above description.


    >> * Reference
    >> The discussion about this patch
    >> http://lists.infradead.org/pipermail/kexec/2009-July/003417.html
    >
    > I'd like to quote your comment:
    >
    >>> I tried to test a kdump on linux-2.6.31-rc1 *without* a kernel parameter
    >>> "oops=panic" by `echo c > /proc/sysrq-trigger`, but a kdump did not work
    >>> because a kdump, which is occurred by `echo c > /proc/sysrq-trigger`, has
    >>> been changed to a NULL pointer error instead of calling crash_kexec()
    >>> since linux-2.6.31-rc1.
    >
    > So the real problem is that kdump is not triggered by the NULL pointer oops
    > if !panic_on_oops, isn't it?
    >
    > It seems that you should report this trouble of sysrq-c as a regression.

    I don't think this problem is a regression of sysrq-c.
    This change of sysrq-c looks reasonable to me. Because sysrq-c is used
    for the test of kdump, and its code path has been changed to the same
    path as a kdump on oops (a real problem, not test).
    So we can test a kdump by a real oops, that is good to me.
    As a result, I could find this problem a kdump is not enabled without
    "oops=panic".


    >> Signed-off-by: Ken'ichi Ohmichi <oomichi@mxs.nes.nec.co.jp>
    >> Acked-by: Simon Horman <horms@verge.net.au>
    >> ---
    >> --- a/kernel/kexec.c 2009-07-08 12:30:26.000000000 +0900
    >> +++ b/kernel/kexec.c 2009-07-08 12:38:08.000000000 +0900
    >> @@ -57,6 +57,8 @@ struct resource crashk_res = {
    >>
    >> int kexec_should_crash(struct task_struct *p)
    >> {
    >> + if (kexec_crash_image)
    >> + return 1;
    >> if (in_interrupt() || !p->pid || is_global_init(p) || panic_on_oops)
    >> return 1;
    >> return 0;
    >
    > I think kexec cannot crash if there is no image, right?
    >
    > Then:
    >
    > if (kexec_crash_image)
    > return 1;
    > return 0;
    >
    > or
    >
    > return (kexec_crash_image) ? 1 : 0;
    >
    > or
    >
    > since crash_kexec() is nop if !kexec_crash_image,
    > replace all:
    > if (kexec_should_crash(p))
    > crash_kexec(reg);
    > at everywhere in kernel to a simple line:
    > crash_kexec(reg);
    > and remove kexec_should_crash() completely
    >
    > would be better fix.

    Good point, I like the first option because it is safe that a caller of
    crash_kexec() checks it. That is not a strong opinion ;-)


    Thanks
    Ken'ichi Ohmichi


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