RE: Re: [V6 PATCH 1/6] panic/x86: Fix re-entrance problem due to panic on NMI

["河合英宏 / KAWAI，HIDEHIRO" <hidehiro.kawai.ez@hitachi.com>]

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> From: Borislav Petkov [mailto:bp@alien8.de]
[...]
> Looks better.
> 
> Did some comments cleanup and nmi_panic() macro reformatting so that it
> is more readable and ended up applying this:

Thanks a lot!

Hidehiro Kawai
Hitachi, Ltd. Research & Development Group

> ---
> From: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
> Date: Thu, 10 Dec 2015 10:46:26 +0900
> Subject: [PATCH] panic, x86: Fix re-entrance problem due to panic on NMI
> 
> If panic on NMI happens just after panic() on the same CPU, panic() is
> recursively called. Kernel stalls, as a result, after failing to acquire
> panic_lock.
> 
> To avoid this problem, don't call panic() in NMI context if we've
> already entered panic().
> 
> For that, introduce nmi_panic() macro to reduce code duplication. In
> the case of panic on NMI, don't return from NMI handlers if another CPU
> already panicked.
> 
> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Cc: Aaron Tomlin <atomlin@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Chris Metcalf <cmetcalf@ezchip.com>
> Cc: David Hildenbrand <dahi@linux.vnet.ibm.com>
> Cc: Don Zickus <dzickus@redhat.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Gobinda Charan Maji <gobinda.cemk07@gmail.com>
> Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Javi Merino <javi.merino@arm.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: kexec@lists.infradead.org
> Cc: linux-doc@vger.kernel.org
> Cc: lkml <linux-kernel@vger.kernel.org>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Michal Nazarewicz <mina86@mina86.com>
> Cc: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Prarit Bhargava <prarit@redhat.com>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Seth Jennings <sjenning@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ulrich Obergfell <uobergfe@redhat.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Link: http://lkml.kernel.org/r/20151210014626.25437.13302.stgit@softrs
> [ Cleanup comments, fixup formatting. ]
> Signed-off-by: Borislav Petkov <bp@suse.de>
> ---
>  arch/x86/kernel/nmi.c  | 16 ++++++++++++----
>  include/linux/kernel.h | 20 ++++++++++++++++++++
>  kernel/panic.c         | 16 +++++++++++++---
>  kernel/watchdog.c      |  2 +-
>  4 files changed, 46 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
> index 697f90db0e37..292a24bd0553 100644
> --- a/arch/x86/kernel/nmi.c
> +++ b/arch/x86/kernel/nmi.c
> @@ -231,7 +231,7 @@ pci_serr_error(unsigned char reason, struct pt_regs *regs)
>  #endif
> 
>  	if (panic_on_unrecovered_nmi)
> -		panic("NMI: Not continuing");
> +		nmi_panic("NMI: Not continuing");
> 
>  	pr_emerg("Dazed and confused, but trying to continue\n");
> 
> @@ -255,8 +255,16 @@ io_check_error(unsigned char reason, struct pt_regs *regs)
>  		 reason, smp_processor_id());
>  	show_regs(regs);
> 
> -	if (panic_on_io_nmi)
> -		panic("NMI IOCK error: Not continuing");
> +	if (panic_on_io_nmi) {
> +		nmi_panic("NMI IOCK error: Not continuing");
> +
> +		/*
> +		 * If end up here, it means we have received an NMI while
> +		 * processing panic(). Simply return without delaying and
> +		 * re-enabling NMI.
> +		 */
> +		return;
> +	}
> 
>  	/* Re-enable the IOCK line, wait for a few seconds */
>  	reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK;
> @@ -297,7 +305,7 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
> 
>  	pr_emerg("Do you have a strange power saving mode enabled?\n");
>  	if (unknown_nmi_panic || panic_on_unrecovered_nmi)
> -		panic("NMI: Not continuing");
> +		nmi_panic("NMI: Not continuing");
> 
>  	pr_emerg("Dazed and confused, but trying to continue\n");
>  }
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 350dfb08aee3..750cc5c7c999 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -446,6 +446,26 @@ extern int sysctl_panic_on_stackoverflow;
>  extern bool crash_kexec_post_notifiers;
> 
>  /*
> + * panic_cpu is used for synchronizing panic() and crash_kexec() execution. It
> + * holds a CPU number which is executing panic() currently. A value of
> + * PANIC_CPU_INVALID means no CPU has entered panic() or crash_kexec().
> + */
> +extern atomic_t panic_cpu;
> +#define PANIC_CPU_INVALID	-1
> +
> +/*
> + * A variant of panic() called from NMI context. We return if we've already
> + * panicked on this CPU.
> + */
> +#define nmi_panic(fmt, ...)						\
> +do {									\
> +	int cpu = raw_smp_processor_id();				\
> +									\
> +	if (atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu) != cpu)	\
> +		panic(fmt, ##__VA_ARGS__);				\
> +} while (0)
> +
> +/*
>   * Only to be used by arch init code. If the user over-wrote the default
>   * CONFIG_PANIC_TIMEOUT, honor it.
>   */
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 4b150bc0c6c1..3344524cf6ff 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -61,6 +61,8 @@ void __weak panic_smp_self_stop(void)
>  		cpu_relax();
>  }
> 
> +atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID);
> +
>  /**
>   *	panic - halt the system
>   *	@fmt: The text string to print
> @@ -71,17 +73,17 @@ void __weak panic_smp_self_stop(void)
>   */
>  void panic(const char *fmt, ...)
>  {
> -	static DEFINE_SPINLOCK(panic_lock);
>  	static char buf[1024];
>  	va_list args;
>  	long i, i_next = 0;
>  	int state = 0;
> +	int old_cpu, this_cpu;
> 
>  	/*
>  	 * Disable local interrupts. This will prevent panic_smp_self_stop
>  	 * from deadlocking the first cpu that invokes the panic, since
>  	 * there is nothing to prevent an interrupt handler (that runs
> -	 * after the panic_lock is acquired) from invoking panic again.
> +	 * after setting panic_cpu) from invoking panic() again.
>  	 */
>  	local_irq_disable();
> 
> @@ -94,8 +96,16 @@ void panic(const char *fmt, ...)
>  	 * multiple parallel invocations of panic, all other CPUs either
>  	 * stop themself or will wait until they are stopped by the 1st CPU
>  	 * with smp_send_stop().
> +	 *
> +	 * `old_cpu == PANIC_CPU_INVALID' means this is the 1st CPU which
> +	 * comes here, so go ahead.
> +	 * `old_cpu == this_cpu' means we came from nmi_panic() which sets
> +	 * panic_cpu to this CPU.  In this case, this is also the 1st CPU.
>  	 */
> -	if (!spin_trylock(&panic_lock))
> +	this_cpu = raw_smp_processor_id();
> +	old_cpu  = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
> +
> +	if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu)
>  		panic_smp_self_stop();
> 
>  	console_verbose();
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 18f34cf75f74..b9be18fae154 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -351,7 +351,7 @@ static void watchdog_overflow_callback(struct perf_event *event,
>  			trigger_allbutself_cpu_backtrace();
> 
>  		if (hardlockup_panic)
> -			panic("Hard LOCKUP");
> +			nmi_panic("Hard LOCKUP");
> 
>  		__this_cpu_write(hard_watchdog_warn, true);
>  		return;
> --
> 2.3.5
> 
> --
> Regards/Gruss,
>     Boris.
> 
> ECO tip #101: Trim your mails when you reply.
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