Commit-ID: 8762705ad4ac860bb78434409df463d02ac8f027 Gitweb: http://git.kernel.org/tip/8762705ad4ac860bb78434409df463d02ac8f027 Author: Paul E. McKenney <paul.mckenney@xxxxxxxxxx> AuthorDate: Wed, 11 Jan 2012 16:59:01 -0800 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Tue, 21 Feb 2012 09:03:42 -0800 rcu: Inform RCU of irq_exit() activity This is a port to TINY_RCU of Peter Zijlstra's commit #ec433f0c5 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); This can be triggered 'easily' 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. It is also necessary to delay the ->rcu_read_lock_nesting decrement until after rcu_read_unlock_special(). This delay is handled by the commit "Protect __rcu_read_unlock() against scheduler-using irq handlers". Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- kernel/rcutiny_plugin.h | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 95df60e..387c275 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -570,7 +570,7 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) rcu_preempt_cpu_qs(); /* Hardware IRQ handlers cannot block. */ - if (in_irq()) { + if (in_irq() || in_serving_softirq()) { local_irq_restore(flags); return; } -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html