From 82aa9a1829199233f9bdaf26e2ee271114f4701e Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Thu, 5 Feb 2009 15:23:08 +0100 Subject: [PATCH] perfcounters: fix "perf counters kills oprofile" bug, v2 Impact: fix kernel crash Both oprofile and perfcounters register an NMI die handler, but only one can handle the NMI. Conveniently, oprofile unregisters it's notifier when not actively in use, so setting it's notifier priority higher than perfcounter's allows oprofile to borrow the NMI for the duration of it's run. Tested/works both as module and built-in. While testing, I found that if kerneltop was generating NMIs at very high frequency, the kernel may panic when oprofile registered it's handler. This turned out to be because oprofile registers it's handler before reset_value has been allocated, so if an NMI comes in while it's still setting up, kabOom. Rather than try more invasive changes, I followed the lead of other places in op_model_ppro.c, and simply returned in that highly unlikely event. (debug warnings attached) Signed-off-by: Mike Galbraith Signed-off-by: Ingo Molnar --- arch/x86/oprofile/op_model_ppro.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/oprofile/op_model_ppro.c b/arch/x86/oprofile/op_model_ppro.c index 07c9145..85eb626 100644 --- a/arch/x86/oprofile/op_model_ppro.c +++ b/arch/x86/oprofile/op_model_ppro.c @@ -126,6 +126,13 @@ static int ppro_check_ctrs(struct pt_regs * const regs, u64 val; int i; + /* + * This can happen if perf counters are in use when + * we steal the die notifier NMI. + */ + if (unlikely(!reset_value)) + goto out; + for (i = 0 ; i < num_counters; ++i) { if (!reset_value[i]) continue; @@ -136,6 +143,7 @@ static int ppro_check_ctrs(struct pt_regs * const regs, } } +out: /* Only P6 based Pentium M need to re-unmask the apic vector but it * doesn't hurt other P6 variant */ apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED); -- 2.7.4