[PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>]

Prevent crash_kexec() from deadlocking of ioapic_lock. When crash_kexec()
is executed on a cpu, the cpu will get ioapic_lock in disable_IO_APIC().
So if the cpu gets NMI while locking ioapic_lock, a deadlock wiil happen.
In this patch, ioapic_lock is initialized before disable_IO_APIC().

To confirm this deadlocking, you'll set up as follows:

1. Add mdelay(1000) after raw_spin_lock_irqsave() in
   native_ioapic_set_affinity()@arch/x86/kernel/apic/io_apic.c

   Although the deadlocking can occur without this modification, it will
  increase the potential of the deadlocking 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 of 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: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
---
 arch/x86/include/asm/apic.h    |    2 ++
 arch/x86/kernel/apic/io_apic.c |    5 +++++
 arch/x86/kernel/crash.c        |    4 ++++
 3 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index f8119b5..ddb06af 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_lock_init(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..2816c07 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_lock_init(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..ea039d5 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -129,6 +129,10 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 
 	lapic_shutdown();
 #if defined(CONFIG_X86_IO_APIC)
+	/*
+	 * Prevent crash_kexec() from deadlocking of ioapic_lock.
+	 */
+	ioapic_lock_init();
 	disable_IO_APIC();
 #endif
 #ifdef CONFIG_HPET_TIMER