panic, x86: Fix re-entrance problem due to panic on NMI

[linux-2.6-block.git] / kernel / panic.c

diff --git a/kernel/panic.c b/kernel/panic.c
index 4b150bc0c6c111ee09f783eaa6aa101339f6ceec..3344524cf6ffd658c901b383af317aa095e4cff0 100644 (file)
--- 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();