If panic on NMI happens just after panic() on the same CPU, panic()
is recursively called. As the result, it stalls on panic_lock.
To avoid this problem, don't call panic() in NMI context if
we've already entered panic() (i.e. we hold panic_lock).
Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
arch/x86/kernel/nmi.c | 18 ++++++++++++------
include/linux/kernel.h | 4 ++++
kernel/panic.c | 33 +++++++++++++++++++++++++--------
3 files changed, 41 insertions(+), 14 deletions(-)
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index d05bd2e..c14b23f 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -230,8 +230,8 @@ void unregister_nmi_handler(unsigned int type, const char *name)
}
#endif
- if (panic_on_unrecovered_nmi)
- panic("NMI: Not continuing");
+ if (panic_on_unrecovered_nmi && spin_trylock(&panic_lock))
+ __panic("NMI: Not continuing");
pr_emerg("Dazed and confused, but trying to continue\n");
@@ -255,8 +255,12 @@ void unregister_nmi_handler(unsigned int type, const char *name)
reason, smp_processor_id());
show_regs(regs);
- if (panic_on_io_nmi)
- panic("NMI IOCK error: Not continuing");
+ if (panic_on_io_nmi) {
+ if (spin_trylock(&panic_lock))
+ __panic("NMI IOCK error: Not continuing");
+ else
+ return; /* We don't want to wait and re-enable NMI */
+ }
/* Re-enable the IOCK line, wait for a few seconds */
reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK;
@@ -296,8 +300,10 @@ void unregister_nmi_handler(unsigned int type, const char *name)
reason, smp_processor_id());
pr_emerg("Do you have a strange power saving mode enabled?\n");
- if (unknown_nmi_panic || panic_on_unrecovered_nmi)
- panic("NMI: Not continuing");
+ if (unknown_nmi_panic || panic_on_unrecovered_nmi) {
+ if (spin_trylock(&panic_lock))
+ __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 5582410..be430dc 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -250,11 +250,15 @@ static inline u32 reciprocal_scale(u32 val, u32 ep_ro)
static inline void might_fault(void) { }
#endif
+typedef struct spinlock spinlock_t;
+extern spinlock_t panic_lock;
extern struct atomic_notifier_head panic_notifier_list;
extern long (*panic_blink)(int state);
__printf(1, 2)
void panic(const char *fmt, ...)
__noreturn __cold;
+void __panic(char *msg)
+ __noreturn __cold;
extern void oops_enter(void);
extern void oops_exit(void);
void print_oops_end_marker(void);
diff --git a/kernel/panic.c b/kernel/panic.c
index 04e91ff..3c8338b 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -60,6 +60,8 @@ void __weak panic_smp_self_stop(void)
cpu_relax();
}
+DEFINE_SPINLOCK(panic_lock);
+
/**
* panic - halt the system
* @fmt: The text string to print
@@ -70,11 +72,8 @@ 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;
/*
* Disable local interrupts. This will prevent panic_smp_self_stop
@@ -97,12 +96,30 @@ void panic(const char *fmt, ...)
if (!spin_trylock(&panic_lock))
panic_smp_self_stop();
- console_verbose();
- bust_spinlocks(1);
va_start(args, fmt);
vsnprintf(buf, sizeof(buf), fmt, args);
va_end(args);
- pr_emerg("Kernel panic - not syncing: %s\n", buf);
+
+ __panic(buf);
+}
+
+/**
+ * __panic - no lock version of panic
+ * @msg: The text string to print
+ *
+ * Normally, please use panic(). This function can be used
+ * only if panic_lock has already been held.
+ *
+ * This function never returns.
+ */
+void __panic(char *msg)
+{
+ long i, i_next = 0;
+ int state = 0;
+
+ console_verbose();
+ bust_spinlocks(1);
+ pr_emerg("Kernel panic - not syncing: %s\n", msg);
#ifdef CONFIG_DEBUG_BUGVERBOSE
/*
* Avoid nested stack-dumping if a panic occurs during oops processing
@@ -131,7 +148,7 @@ void panic(const char *fmt, ...)
* Run any panic handlers, including those that might need to
* add information to the kmsg dump output.
*/
- atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
+ atomic_notifier_call_chain(&panic_notifier_list, 0, msg);
kmsg_dump(KMSG_DUMP_PANIC);
@@ -190,7 +207,7 @@ void panic(const char *fmt, ...)
disabled_wait(caller);
}
#endif
- pr_emerg("---[ end Kernel panic - not syncing: %s\n", buf);
+ pr_emerg("---[ end Kernel panic - not syncing: %s\n", msg);
local_irq_enable();
for (i = 0; ; i += PANIC_TIMER_STEP) {
touch_softlockup_watchdog();
--
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