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Message-Id: <1450088355-27996-2-git-send-email-bp@alien8.de>
Date: Mon, 14 Dec 2015 11:19:09 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ingo Molnar <mingo@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/7] panic, x86: Fix re-entrance problem due to panic on NMI
From: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
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@...achi.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Aaron Tomlin <atomlin@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Baoquan He <bhe@...hat.com>
Cc: Chris Metcalf <cmetcalf@...hip.com>
Cc: David Hildenbrand <dahi@...ux.vnet.ibm.com>
Cc: Don Zickus <dzickus@...hat.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Gobinda Charan Maji <gobinda.cemk07@...il.com>
Cc: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Javi Merino <javi.merino@....com>
Cc: Jonathan Corbet <corbet@....net>
Cc: kexec@...ts.infradead.org
Cc: linux-doc@...r.kernel.org
Cc: lkml <linux-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Michal Nazarewicz <mina86@...a86.com>
Cc: Nicolas Iooss <nicolas.iooss_linux@....org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Rusty Russell <rusty@...tcorp.com.au>
Cc: Seth Jennings <sjenning@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ulrich Obergfell <uobergfe@...hat.com>
Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: Vivek Goyal <vgoyal@...hat.com>
Link: http://lkml.kernel.org/r/20151210014626.25437.13302.stgit@softrs
[ Cleanup comments, fixup formatting. ]
Signed-off-by: Borislav Petkov <bp@...e.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..fca87938d739 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 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");
}
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
--
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