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Message-ID: <20151210014626.25437.13302.stgit@softrs>
Date: Thu, 10 Dec 2015 10:46:26 +0900
From: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
To: Jonathan Corbet <corbet@....net>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
"H. Peter Anvin" <hpa@...or.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vivek Goyal <vgoyal@...hat.com>
Cc: Baoquan He <bhe@...hat.com>, linux-doc@...r.kernel.org,
x86@...nel.org, kexec@...ts.infradead.org,
linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
Michal Hocko <mhocko@...nel.org>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: [V6 PATCH 1/6] 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. As the result, it stalls after failing to
acquire panic_lock.
To avoid this problem, don't call panic() in NMI context if
we've already entered panic().
V6:
- Add a comment about panic_cpu
- Replace the magic number -1 for panic_cpu with a macro
V4:
- Improve comments in io_check_error() and panic()
V3:
- 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
V2:
- Use atomic_cmpxchg() instead of current spin_trylock() to
exclude concurrent accesses to the panic routines
- Don't introduce no-lock version of panic()
Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Michal Hocko <mhocko@...nel.org>
---
arch/x86/kernel/nmi.c | 16 ++++++++++++----
include/linux/kernel.h | 21 +++++++++++++++++++++
kernel/panic.c | 15 ++++++++++++---
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 697f90d..5131714 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 return from nmi_panic(), it means we have received
+ * NMI while processing panic(). So, simply return without
+ * a delay 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 350dfb0..db66867 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -446,6 +446,27 @@ extern int sysctl_panic_on_stackoverflow;
extern bool crash_kexec_post_notifiers;
/*
+ * panic_cpu holds a panicking CPU number and is used for exclusive
+ * execution of panic and crash_kexec routines. If the value is
+ * PANIC_CPU_INVALID, it means that none of 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.
+ * If we've already panicked on this CPU, return from here.
+ */
+#define nmi_panic(fmt, ...) \
+ do { \
+ int this_cpu = raw_smp_processor_id(); \
+ if (atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu) \
+ != this_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 4b150bc..3261e2d 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 +96,15 @@ 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 18f34cf..b9be18f 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;
--
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