linux-kernel - [PATCH 5/7] i386, dumpstack: use x86_64's method to account die_nest

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Date:	Wed, 22 Oct 2008 12:00:12 +0200
From:	Alexander van Heukelum <heukelum@...tmail.fm>
To:	Neil Horman <nhorman@...driver.com>, Ingo Molnar <mingo@...e.hu>,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	vgoyal@...hat.com, hbabu@...ibm.com, hpa@...or.com,
	akpm@...ux-foundation.org,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	ebiederm@...ssion.com, tglx@...utronix.de
Cc:	Alexander van Heukelum <heukelum@...tmail.fm>
Subject: [PATCH 5/7] i386, dumpstack: use x86_64's method to account die_nest_count

oops_begin/oops_end should always be used in pairs. On x86_64
oops_begin increments die_nest_count, and oops_end decrements
die_nest_count. Doing this makes oops_begin and oops_end equal
to the x86_64 versions.

Signed-off-by: Alexander van Heukelum <heukelum@...tmail.fm>
---
 arch/x86/kernel/dumpstack_32.c |   29 +++++++++++++++++------------
 1 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index a29b88f..7c7d691 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -289,21 +289,24 @@ static unsigned int die_nest_count;
 
 unsigned __kprobes long oops_begin(void)
 {
+	int cpu;
 	unsigned long flags;
 
 	oops_enter();
 
-	if (die_owner != raw_smp_processor_id()) {
-		console_verbose();
-		raw_local_irq_save(flags);
-		__raw_spin_lock(&die_lock);
-		die_owner = smp_processor_id();
-		die_nest_count = 0;
-		bust_spinlocks(1);
-	} else {
-		raw_local_irq_save(flags);
+	/* racy, but better than risking deadlock. */
+	raw_local_irq_save(flags);
+	cpu = smp_processor_id();
+	if (!__raw_spin_trylock(&die_lock)) {
+		if (cpu == die_owner)
+			/* nested oops. should stop eventually */;
+		else
+			__raw_spin_lock(&die_lock);
 	}
 	die_nest_count++;
+	die_owner = cpu;
+	console_verbose();
+	bust_spinlocks(1);
 	return flags;
 }
 
@@ -315,13 +318,15 @@ void __kprobes oops_end(unsigned long flags, struct pt_regs *regs, int signr)
 	bust_spinlocks(0);
 	die_owner = -1;
 	add_taint(TAINT_DIE);
-	__raw_spin_unlock(&die_lock);
+	die_nest_count--;
+	if (!die_nest_count)
+		/* Nest count reaches zero, release the lock. */
+		__raw_spin_unlock(&die_lock);
 	raw_local_irq_restore(flags);
-
 	oops_exit();
+
 	if (!signr)
 		return;
-
 	if (in_interrupt())
 		panic("Fatal exception in interrupt");
 	if (panic_on_oops)
-- 
1.5.4.3

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