[Xen-devel] [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 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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