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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2011-07-19 15:32:00 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-07-20 10:50:12 -0700
commitec433f0c51527426989ea8a38a856d810d739414 (patch)
tree001550d7b18b3f2b5326da3f9dfd893e31c8dc1c /kernel/softirq.c
parentc5d753a55ac92e09816d410cd17093813f1a904b (diff)
softirq,rcu: Inform RCU of irq_exit() activity
The rcu_read_unlock_special() function relies on in_irq() to exclude scheduler activity from interrupt level. This fails because exit_irq() can invoke the scheduler after clearing the preempt_count() bits that in_irq() uses to determine that it is at interrupt level. This situation can result in failures as follows: $task IRQ SoftIRQ rcu_read_lock() /* do stuff */ <preempt> |= UNLOCK_BLOCKED rcu_read_unlock() --t->rcu_read_lock_nesting irq_enter(); /* do stuff, don't use RCU */ irq_exit(); sub_preempt_count(IRQ_EXIT_OFFSET); invoke_softirq() ttwu(); spin_lock_irq(&pi->lock) rcu_read_lock(); /* do stuff */ rcu_read_unlock(); rcu_read_unlock_special() rcu_report_exp_rnp() ttwu() spin_lock_irq(&pi->lock) /* deadlock */ rcu_read_unlock_special(t); Ed can simply trigger this 'easy' because invoke_softirq() immediately does a ttwu() of ksoftirqd/# instead of doing the in-place softirq stuff first, but even without that the above happens. Cure this by also excluding softirqs from the rcu_read_unlock_special() handler and ensuring the force_irqthreads ksoftirqd/# wakeup is done from full softirq context. [ Alternatively, delaying the ->rcu_read_lock_nesting decrement until after the special handling would make the thing more robust in the face of interrupts as well. And there is a separate patch for that. ] Cc: Thomas Gleixner <tglx@linutronix.de> Reported-and-tested-by: Ed Tomlinson <edt@aei.ca> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/softirq.c')
-rw-r--r--kernel/softirq.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 40cf63ddd4b..fca82c32042 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -315,16 +315,24 @@ static inline void invoke_softirq(void)
{
if (!force_irqthreads)
__do_softirq();
- else
+ else {
+ __local_bh_disable((unsigned long)__builtin_return_address(0),
+ SOFTIRQ_OFFSET);
wakeup_softirqd();
+ __local_bh_enable(SOFTIRQ_OFFSET);
+ }
}
#else
static inline void invoke_softirq(void)
{
if (!force_irqthreads)
do_softirq();
- else
+ else {
+ __local_bh_disable((unsigned long)__builtin_return_address(0),
+ SOFTIRQ_OFFSET);
wakeup_softirqd();
+ __local_bh_enable(SOFTIRQ_OFFSET);
+ }
}
#endif