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 <CPU num> > /proc/irq/<IO-APIC-edge or IO-APIC-fasteoi>/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 <domain>' 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 <yoshihiro.yunomae.ez@hitachi.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: yrl.pp-manager.tt@hitachi.com
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Link: http://lkml.kernel.org/r/20130820070107.28245.83806.stgit@yunodevel
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index f8119b582c3c0b6e724aa4f1552269d2854de904..1d2091a226bcac5b55b05225816bf1f374860c3c 100644 (file)
--- 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 9ed796ccc32ccda58fe9e1d914aa2c7828845d0c..260abc2f9eebda97d39b4108524529320e548a7b 100644 (file)
--- 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 74467feb4dc55b2d4e8495992925efe5a51d77f7..e0e0841eef45dcf4381e28a9618a9c1db203df05 100644 (file)
--- 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