Hello Eric,
On Mon, 2011-10-24 at 10:07 -0700, Eric W. Biederman wrote:
[snip]
> So my second thought is to introduce another atomic variable
> panic_in_progress, visible only in panic. The cpu that sets
> increments panic_in_progress can call smp_send_stop. The rest of
> the cpus can just go into a busy wait. That should stop nasty
> fights about who is going to come out of smp_send_stop first.
So this is a spinlock, no? What about the following patch:
---
kernel/panic.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -59,6 +59,7 @@ EXPORT_SYMBOL(panic_blink);
*/
NORET_TYPE void panic(const char * fmt, ...)
{
+ static DEFINE_SPINLOCK(panic_lock);
static char buf[1024];
va_list args;
long i, i_next = 0;
@@ -68,8 +69,12 @@ NORET_TYPE void panic(const char * fmt,
* It's possible to come here directly from a panic-assertion and
* not have preempt disabled. Some functions called from here want
* preempt to be disabled. No point enabling it later though...
+ *
+ * Only one CPU is allowed to execute the panic code. For multiple
+ * parallel invocations of panic all other CPUs will wait on the
+ * panic_lock. They are stopped afterwards by smp_send_stop().
*/
- preempt_disable();
+ spin_lock(&panic_lock);
console_verbose();
bust_spinlocks(1);
