Some keyhandlers are calling process_pending_softirqs() while holding
a rcu_read_lock(). This is wrong, as process_pending_softirqs() might
activate rcu calls which should not happen inside a rcu_read_lock().
For that purpose modify process_pending_softirqs() to not allow rcu
callback processing when a rcu_read_lock() is being held.
Signed-off-by: Juergen Gross
---
V3:
- add RCU_SOFTIRQ to ignore in process_pending_softirqs_norcu()
(Roger Pau Monné)
V5:
- block rcu processing depending on rch_read_lock() being held or not
(Jan Beulich)
---
xen/common/softirq.c | 12 ++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/xen/common/softirq.c b/xen/common/softirq.c
index b83ad96d6c..00d676b62c 100644
--- a/xen/common/softirq.c
+++ b/xen/common/softirq.c
@@ -29,6 +29,7 @@ static void __do_softirq(unsigned long ignore_mask)
{
unsigned int i, cpu;
unsigned long pending;
+bool rcu_allowed = !(ignore_mask & (1ul << RCU_SOFTIRQ));
for ( ; ; )
{
@@ -38,7 +39,7 @@ static void __do_softirq(unsigned long ignore_mask)
*/
cpu = smp_processor_id();
-if ( rcu_pending(cpu) )
+if ( rcu_allowed && rcu_pending(cpu) )
rcu_check_callbacks(cpu);
if ( ((pending = (softirq_pending(cpu) & ~ignore_mask)) == 0)
@@ -53,9 +54,16 @@ static void __do_softirq(unsigned long ignore_mask)
void process_pending_softirqs(void)
{
+unsigned long ignore_mask = (1ul << SCHEDULE_SOFTIRQ) |
+(1ul << SCHED_SLAVE_SOFTIRQ);
+
+/* Block RCU processing in case of rcu_read_lock() held. */
+if ( preempt_count() )
+ignore_mask |= 1ul << RCU_SOFTIRQ;
+
ASSERT(!in_irq() && local_irq_is_enabled());
/* Do not enter scheduler as it can preempt the calling context. */
-__do_softirq((1ul << SCHEDULE_SOFTIRQ) | (1ul << SCHED_SLAVE_SOFTIRQ));
+__do_softirq(ignore_mask);
}
void do_softirq(void)
--
2.16.4
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