linux-kernel - Re: [git pull] scheduler/misc fixes

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Message-Id: <20080425.005738.114887644.davem@davemloft.net>
Date:	Fri, 25 Apr 2008 00:57:38 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	a.p.zijlstra@...llo.nl
Cc:	mingo@...e.hu, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, alan@...rguk.ukuu.org.uk,
	tglx@...utronix.de
Subject: Re: [git pull] scheduler/misc fixes

From: Peter Zijlstra <a.p.zijlstra@...llo.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);
 	}
 }
 


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