linux-kernel - [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

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Date:	Thu,  1 Sep 2011 17:55:01 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM <kvm@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>

We need to make sure interrupts are disabled while we're relying on the
contents of the per-cpu lock_waiting values, otherwise an interrupt
handler could come in, try to take some other lock, block, and overwrite
our values.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 arch/x86/xen/spinlock.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 4c46144..2ed5d05 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -98,6 +98,7 @@ static void xen_lock_spinning(struct arch_spinlock *lock, unsigned want)
 	struct xen_lock_waiting *w = &__get_cpu_var(lock_waiting);
 	int cpu = smp_processor_id();
 	u64 start;
+	unsigned long flags;
 
 	/* If kicker interrupts not initialized yet, just spin */
 	if (irq == -1)
@@ -105,6 +106,10 @@ static void xen_lock_spinning(struct arch_spinlock *lock, unsigned want)
 
 	start = spin_time_start();
 
+	/* Make sure interrupts are disabled to ensure that these
+	   per-cpu values are not overwritten. */
+	local_irq_save(flags);
+
 	w->want = want;
 	w->lock = lock;
 
@@ -139,6 +144,9 @@ static void xen_lock_spinning(struct arch_spinlock *lock, unsigned want)
 out:
 	cpumask_clear_cpu(cpu, &waiting_cpus);
 	w->lock = NULL;
+
+	local_irq_restore(flags);
+
 	spin_time_accum_blocked(start);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
-- 
1.7.6

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