From: Paul Mackerras <paulus@samba.org>
When taking a cpu offline, once the cpu has been removed from
cpu_online_map, it is not supposed to service any more interrupts. This
presents a problem on ppc64 because we cannot truly disable the
decrementer. There used to be cpu_is_offline() checks in several scheduler
functions (e.g. rebalance_tick()) which papered over this issue, but these
checks were removed recently. So with recent 2.6 kernels, an attempt to
offline a cpu can result in a crash in find_busiest_group(). This patch
prevents such crashes.
Signed-off-by: Nathan Lynch <nathanl@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/arch/ppc64/kernel/time.c | 15 ++++++++++++++-
1 files changed, 14 insertions(+), 1 deletion(-)
diff -puN arch/ppc64/kernel/time.c~ppc64-dont-call-scheduler-on-offline-cpu arch/ppc64/kernel/time.c
--- 25/arch/ppc64/kernel/time.c~ppc64-dont-call-scheduler-on-offline-cpu Tue Aug 17 14:51:28 2004
+++ 25-akpm/arch/ppc64/kernel/time.c Tue Aug 17 14:51:28 2004
@@ -48,6 +48,7 @@
#include <linux/time.h>
#include <linux/init.h>
#include <linux/profile.h>
+#include <linux/cpu.h>
#include <asm/segment.h>
#include <asm/io.h>
@@ -245,8 +246,20 @@ int timer_interrupt(struct pt_regs * reg
while (lpaca->next_jiffy_update_tb <= (cur_tb = get_tb())) {
#ifdef CONFIG_SMP
- smp_local_timer_interrupt(regs);
+ /*
+ * We cannot disable the decrementer, so in the period
+ * between this cpu's being marked offline in cpu_online_map
+ * and calling stop-self, it is taking timer interrupts.
+ * Avoid calling into the scheduler rebalancing code if this
+ * is the case.
+ */
+ if (!cpu_is_offline(cpu))
+ smp_local_timer_interrupt(regs);
#endif
+ /*
+ * No need to check whether cpu is offline here; boot_cpuid
+ * should have been fixed up by now.
+ */
if (cpu == boot_cpuid) {
write_seqlock(&xtime_lock);
tb_last_stamp = lpaca->next_jiffy_update_tb;
_