Re: [git pull] scheduler/misc fixes

David Miller
2008-04-25T07:57:48Z

From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri, 25 Apr 2008 09:48:30 +0200

> c) there are 'IPI' handlers on SPARC64 that look like they can wake
> the CPU from idle sleep but do not appear to call irq_enter() which
> has the above patch's touch_softlock_watchdog() in its callchain.
>
> tl0_irq1: TRAP_IRQ(smp_call_function_client, 1)
> tl0_irq2: TRAP_IRQ(smp_receive_signal_client, 2)
> tl0_irq3: TRAP_IRQ(smp_penguin_jailcell, 3)
> tl0_irq4: TRAP_IRQ(smp_new_mmu_context_version_client, 4)
>
>
>
> So the current working thesis is that the bug in a) hides a real problem
> not quite fixed by b) and exploited by c).

The equivalent to smp_receive_signal_client() on x86
(smp_reschedule_interrupt) doesn't do an irq_enter() either.

However x86 does do an irq_enter() for smp_call_function() interrupt
handling.

What is the rule in these cases?

Anyways, does the following patch fix the problem?

diff --git a/arch/sparc64/kernel/smp.c b/arch/sparc64/kernel/smp.c
index 524b889..bf4ef84 100644
--- a/arch/sparc64/kernel/smp.c
+++ b/arch/sparc64/kernel/smp.c
@@ -866,14 +866,21 @@ void smp_call_function_client(int irq, struct pt_regs *regs)
void *info = call_data->info;

clear_softint(1 << irq);
+
+ irq_enter();
+
+ if (!call_data->wait) {
+ /* let initiator proceed after getting data */
+ atomic_inc(&call_data->finished);
+ }
+
+ func(info);
+
+ irq_exit();
+
if (call_data->wait) {
/* let initiator proceed only after completion */
- func(info);
- atomic_inc(&call_data->finished);
- } else {
- /* let initiator proceed after getting data */
atomic_inc(&call_data->finished);
- func(info);
}
}