[PATCH V2] [BUGFIX] crash/ioapic: Prevent crash_kexec() fromdeadlocking on ioapic_lock

[Yoshihiro YUNOMAE]

Prevent crash_kexec() from deadlocking on 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 will happen.
In this patch, ioapic_lock is initialized before disable_IO_APIC().

To confirm this deadlock, 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 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().

Changes in V2: Fix typos, change ioapic_lock_init() to ioapic_zap_locks(),
               and change "#if defined(CONFIG_X86_IO_APIC)" to
               "#ifdef CONFIG_X86_IO_APIC".

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Seiji Aguchi <seiji.aguchi@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <sebastian@xxxxxxxxxxxxx>
Cc: Joerg Roedel <joro@xxxxxxxxxx>
Cc: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
---
 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

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