[PATCH] Avoid triggering the softlockup BUG when offline for too long.

[Glauber de Oliveira Costa <gcosta@redhat.com>]

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After being offline for a long time, the softlockup  watchdog triggers
a BUG() on our faces. This is expected, as in fact, we spent more than
a fixed 10*HZ amount of time without touching the watchdog.

However, by inspecting the contents of RUNSTATE_offline, we can gain
awareness of the fact, and do better than that. This patch fixes it.

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>


-- 
Glauber de Oliveira Costa
Red Hat Inc.
"Free as in Freedom"

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# HG changeset patch
# User gcosta@redhat.com
# Date 1164376767 18000
# Node ID 0f235d94eeabbca64c14ae6d5ae3708870522f60
# Parent  47fcd5f768fef50cba2fc6dbadc7b75de55e88a5
[LINUX] Avoid triggering the softlockup BUG when offline for too long.

After being offline for a long time, the softlockup  watchdog triggers
a BUG() on our faces. This is expected, as in fact, we spent more than
a fixed 10*HZ amount of time without touching the watchdog.

However, by inspecting the contents of RUNSTATE_offline, we can gain
awareness of the fact, and do better than that. This patch fixes it.

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>

diff -r 47fcd5f768fe -r 0f235d94eeab linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c
--- a/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c	Fri Nov 17 08:30:43 2006 -0500
+++ b/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c	Fri Nov 24 08:59:27 2006 -0500
@@ -129,6 +129,8 @@ static DEFINE_PER_CPU(u64, processed_sys
 /* How much CPU time was spent blocked and how much was 'stolen'? */
 static DEFINE_PER_CPU(u64, processed_stolen_time);
 static DEFINE_PER_CPU(u64, processed_blocked_time);
+/* How much time did we spend offline? */
+static DEFINE_PER_CPU(u64, offline_time);
 
 /* Current runstate of each CPU (updated automatically by the hypervisor). */
 static DEFINE_PER_CPU(struct vcpu_runstate_info, runstate);
@@ -607,7 +609,7 @@ EXPORT_SYMBOL(profile_pc);
 
 irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 {
-	s64 delta, delta_cpu, stolen, blocked;
+	s64 delta, delta_cpu, stolen, blocked, offline;
 	u64 sched_time;
 	int i, cpu = smp_processor_id();
 	struct shadow_time_info *shadow = &per_cpu(shadow_time, cpu);
@@ -636,6 +638,8 @@ irqreturn_t timer_interrupt(int irq, voi
 				per_cpu(processed_stolen_time, cpu);
 			blocked = runstate->time[RUNSTATE_blocked] -
 				per_cpu(processed_blocked_time, cpu);
+			offline = runstate->time[RUNSTATE_offline] -
+				per_cpu(offline_time, cpu);
 			barrier();
 		} while (sched_time != runstate->state_entry_time);
 	} while (!time_values_up_to_date(cpu));
@@ -710,6 +714,13 @@ irqreturn_t timer_interrupt(int irq, voi
 					    (cputime_t)delta_cpu);
 	}
 
+	/* We know we were offline for too long, avoid triggering the 
+	 * softlockup_tick bug */
+	if ((offline > 10*HZ)) {
+		touch_softlockup_watchdog();
+		per_cpu(offline_time, cpu) += offline;
+	}
+
 	/* Local timer processing (see update_process_times()). */
 	run_local_timers();
 	if (rcu_pending(cpu))
@@ -734,6 +745,8 @@ static void init_missing_ticks_accountin
 		runstate->time[RUNSTATE_blocked];
 	per_cpu(processed_stolen_time, cpu) =
 		runstate->time[RUNSTATE_runnable] +
+		runstate->time[RUNSTATE_offline];
+	per_cpu(offline_time, cpu) =
 		runstate->time[RUNSTATE_offline];
 }
 

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