crash/ioapic: Prevent crash_kexec() from deadlocking on ioapic_lock
Subsystems (2)
PATCH v2 1/1 crash/ioapic: 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 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-mkconfig4. 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".
--- 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(-)
arch/x86/include/asm/apic.h +2 -0
@@ -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 */
arch/x86/kernel/apic/io_apic.c +5 -0
@@ -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;
arch/x86/kernel/crash.c +3 -1
@@ -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
tip-bot for Yoshihiro YUNOMAE
merge bot[tip:x86/apic] x86/ioapic/kcrash: Prevent crash_kexec() from deadlocking on ioapic_lock
x86/ioapic/kcrash: Prevent crash_kexec() from deadlocking on ioapic_lock
Commit-ID: 17405453f4ad0220721a29978692081be6392b8f Gitweb: http://git.kernel.org/tip/17405453f4ad0220721a29978692081be6392b8f Author: Yoshihiro YUNOMAE <[email protected]> AuthorDate: Tue, 20 Aug 2013 16:01:07 +0900 Committer: Ingo Molnar <[email protected]> CommitDate: Tue, 20 Aug 2013 09:26:33 +0200
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-mkconfig4. 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().
--- 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(-)
arch/x86/include/asm/apic.h +2 -0
@@ -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 */
arch/x86/kernel/apic/io_apic.c +5 -0
@@ -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;
arch/x86/kernel/crash.c +3 -1
@@ -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