From 17405453f4ad0220721a29978692081be6392b8f Mon Sep 17 00:00:00 2001 From: Yoshihiro YUNOMAE Date: Tue, 20 Aug 2013 16:01:07 +0900 Subject: [PATCH] x86/ioapic/kcrash: Prevent crash_kexec() from deadlocking on ioapic_lock Prevent crash_kexec() from deadlocking on ioapic_lock. When crash_kexec() is executed on a CPU, the CPU will take ioapic_lock in disable_IO_APIC(). So if the cpu gets an NMI while locking ioapic_lock, a deadlock will happen. In this patch, ioapic_lock is zapped/initialized before disable_IO_APIC(). You can reproduce this deadlock the following way: 1. Add mdelay(1000) after raw_spin_lock_irqsave() in native_ioapic_set_affinity()@arch/x86/kernel/apic/io_apic.c Although the deadlock can occur without this modification, it will increase the potential of the deadlock problem. 2. Build and install the kernel 3. Set up the OS which will run panic() and kexec when NMI is injected # echo "kernel.unknown_nmi_panic=1" >> /etc/sysctl.conf # vim /etc/default/grub add "nmi_watchdog=0 crashkernel=256M" in GRUB_CMDLINE_LINUX line # grub2-mkconfig 4. Reboot the OS 5. Run following command for each vcpu on the guest # while true; do echo > /proc/irq//smp_affinitity; done; By running this command, cpus will get ioapic_lock for setting affinity. 6. Inject NMI (push a dump button or execute 'virsh inject-nmi ' if you use VM). After injecting NMI, panic() is called in an nmi-handler context. Then, kexec will normally run in panic(), but the operation will be stopped by deadlock on ioapic_lock in crash_kexec()->machine_crash_shutdown()-> native_machine_crash_shutdown()->disable_IO_APIC()->clear_IO_APIC()-> clear_IO_APIC_pin()->ioapic_read_entry(). Signed-off-by: Yoshihiro YUNOMAE Cc: Andi Kleen Cc: Gleb Natapov Cc: Konrad Rzeszutek Wilk Cc: Joerg Roedel Cc: Marcelo Tosatti Cc: Hidehiro Kawai Cc: Sebastian Andrzej Siewior Cc: Zhang Yanfei Cc: Eric W. Biederman Cc: yrl.pp-manager.tt@hitachi.com Cc: Masami Hiramatsu Cc: Seiji Aguchi Link: http://lkml.kernel.org/r/20130820070107.28245.83806.stgit@yunodevel Signed-off-by: Ingo Molnar --- arch/x86/include/asm/apic.h | 2 ++ arch/x86/kernel/apic/io_apic.c | 5 +++++ arch/x86/kernel/crash.c | 4 +++- 3 files changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h index f8119b5..1d2091a 100644 --- a/arch/x86/include/asm/apic.h +++ b/arch/x86/include/asm/apic.h @@ -715,4 +715,6 @@ static inline void exiting_ack_irq(void) ack_APIC_irq(); } +extern void ioapic_zap_locks(void); + #endif /* _ASM_X86_APIC_H */ diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c index 9ed796c..260abc2 100644 --- a/arch/x86/kernel/apic/io_apic.c +++ b/arch/x86/kernel/apic/io_apic.c @@ -1534,6 +1534,11 @@ void intel_ir_io_apic_print_entries(unsigned int apic, } } +void ioapic_zap_locks(void) +{ + raw_spin_lock_init(&ioapic_lock); +} + __apicdebuginit(void) print_IO_APIC(int ioapic_idx) { union IO_APIC_reg_00 reg_00; diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c index 74467fe..e0e0841 100644 --- a/arch/x86/kernel/crash.c +++ b/arch/x86/kernel/crash.c @@ -128,7 +128,9 @@ void native_machine_crash_shutdown(struct pt_regs *regs) cpu_emergency_svm_disable(); lapic_shutdown(); -#if defined(CONFIG_X86_IO_APIC) +#ifdef CONFIG_X86_IO_APIC + /* Prevent crash_kexec() from deadlocking on ioapic_lock. */ + ioapic_zap_locks(); disable_IO_APIC(); #endif #ifdef CONFIG_HPET_TIMER -- 2.7.4