Messages in this thread | | | Date | Fri, 29 Mar 2013 09:46:40 -0400 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [PATCH] xen: Don't call arch_trigger_all_cpu_backtrace in dom0(pvm) |
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On Fri, Mar 29, 2013 at 03:22:38PM +0800, Zhenzhong Duan wrote: > nmi isn't supported in dom0, fallback to general all cpu backtrace code. > > Without fix, on xapic system, sysrq+l, no backtrace is showed. > On x2apic enabled system, got NULL pointer dereference as below.
Why would the x2APIC or xAPIC make a difference here? The Linux dom0 is not fiddling with the APIC - that is the hypervisor job.
Can you explain to me why x2apic_send_IPI_mask is even set? Wouldn't the Xen version of send_IPI be present? (See xen_smp_ops)
Perhaps it is missing an over-write for the send_IPI_all?
> > SysRq : Show backtrace of all active CPUs > BUG: unable to handle kernel NULL pointer dereference at (null) > IP: [<ffffffff8125e3cb>] memcpy+0xb/0x120 > Call Trace: > [<ffffffff81039633>] ? __x2apic_send_IPI_mask+0x73/0x160 > [<ffffffff8103973e>] x2apic_send_IPI_all+0x1e/0x20 > [<ffffffff8103498c>] arch_trigger_all_cpu_backtrace+0x6c/0xb0 > [<ffffffff81501be4>] ? _raw_spin_lock_irqsave+0x34/0x50 > [<ffffffff8131654e>] sysrq_handle_showallcpus+0xe/0x10 > [<ffffffff8131616d>] __handle_sysrq+0x7d/0x140 > [<ffffffff81316230>] ? __handle_sysrq+0x140/0x140 > [<ffffffff81316287>] write_sysrq_trigger+0x57/0x60 > [<ffffffff811ca996>] proc_reg_write+0x86/0xc0 > [<ffffffff8116dd8e>] vfs_write+0xce/0x190 > [<ffffffff8116e3e5>] sys_write+0x55/0x90 > [<ffffffff8150a242>] system_call_fastpath+0x16/0x1b > > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com> > Tested-by: Tamon Shiose <tamon.shiose@oracle.com> > --- > include/linux/nmi.h | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/include/linux/nmi.h b/include/linux/nmi.h > index db50840..b845757 100644 > --- a/include/linux/nmi.h > +++ b/include/linux/nmi.h > @@ -32,6 +32,8 @@ static inline void touch_nmi_watchdog(void) > #ifdef arch_trigger_all_cpu_backtrace > static inline bool trigger_all_cpu_backtrace(void) > { > + if (xen_domain()) > + return false; > arch_trigger_all_cpu_backtrace(); > > return true; > -- > 1.7.3 >
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