Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 1717f209 authored by Hidehiro Kawai's avatar Hidehiro Kawai Committed by Thomas Gleixner
Browse files

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: default avatarHidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Acked-by: default avatarMichal 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: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent d267b8d6

arch/x86/kernel/nmi.c

+12 −4
Original line number Diff line number Diff line
@@ -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 we end up here, it means we have received an NMI while

		 * processing panic(). Simply return without delaying and

		 * re-enabling NMIs.

		 */

		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");

}

include/linux/kernel.h

+20 −0
Original line number Diff line number Diff line
@@ -445,6 +445,26 @@ 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.

kernel/panic.c

+13 −3
Original line number Diff line number Diff line
@@ -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();

kernel/watchdog.c

+1 −1
Original line number Diff line number Diff line
@@ -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;