* Completely Remove the option STOP_NMI from the kernel. This option

has proven to have a good effect when entering KDB by using a NMI,
but it completely violates all the good rules about interrupts
disabled while holding a spinlock in other occasions.  This can be the
cause of deadlocks on events where a normal IPI_STOP is expected.
* Adds an new IPI called IPI_STOP_HARD on all the supported architectures.
This IPI is responsible for sending a stop message among CPUs using a
privileged channel when disponible. In other cases it just does match a
normal IPI_STOP.
Right now the IPI_STOP_HARD functionality uses a NMI on ia32 and amd64
architectures, while on the other has a normal IPI_STOP effect. It is
responsibility of maintainers to eventually implement an hard stop
when necessary and possible.
* Use the new IPI facility in order to implement a new userend SMP kernel
function called stop_cpus_hard(). That is specular to stop_cpu() but
it does use the privileged channel for the stopping facility.
* Let KDB use the newly introduced function stop_cpus_hard() and leave
stop_cpus() for all the other cases
* Disable interrupts on CPU0 when starting the process of APs suspension.
* Style cleanup and comments adding

This patch should fix the reboot/shutdown deadlocks many users are
constantly reporting on mailing lists.

Please don't forget to update your config file with the STOP_NMI
option removal

Reviewed by:	jhb
Tested by:	pho, bz, rink
Approved by:	re (kib)

1 files changed, 7 insertions, 3 deletions

diff --git a/sys/kern/kern_shutdown.c b/sys/kern/kern_shutdown.c
index 80dda97..0f3a672 100644
--- a/sys/kern/kern_shutdown.c
+++ b/sys/kern/kern_shutdown.c
@@ -412,9 +412,6 @@ boot(int howto)
 	 */
 	EVENTHANDLER_INVOKE(shutdown_post_sync, howto);
 
-	/* XXX This doesn't disable interrupts any more.  Reconsider? */
-	splhigh();
-
 	if ((howto & (RB_HALT|RB_DUMP)) == RB_DUMP && !cold && !dumping) 
 		doadump();
 
@@ -488,6 +485,13 @@ static void
 shutdown_reset(void *junk, int howto)
 {
 
+	/*
+	 * Disable interrupts on CPU0 in order to avoid fast handlers
+	 * to preempt the stopping process and to deadlock against other
+	 * CPUs.
+	 */
+	spinlock_enter();
+
 	printf("Rebooting...\n");
 	DELAY(1000000);	/* wait 1 sec for printf's to complete and be read */
 	/* cpu_boot(howto); */ /* doesn't do anything at the moment */