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 <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Andrew Morton <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Seiji Aguchi <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Zhang Yanfei <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Gleb Natapov <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: [email protected]
Cc: [email protected]
---
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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