On Wed, 12 Apr 2017, Borislav Petkov wrote: > On Wed, Apr 12, 2017 at 08:27:05PM +0000, Verma, Vishal L wrote: > > But isn't the atomic notifier call chain always called in atomic > > context? > > No, it isn't. We're calling it in normal process context in > mce_gen_pool_process() too. > > So this early exit will avoid any sleeping in atomic context. And since > there's nothing you can do about the errors reported in atomic context, > we can actually use that fact.
No, you can't. CONFIG_RCU_PREEMPT=n + CONFIG_PREEMPT_COUNT will disable preemption from within __atomic_notifier_call_chain() via rcu_read_lock(). Ergo you wont ever enter the handler. The behaviour in the RCU code is inconsistent. CONFIG_RCU_PREEMPT=y does obviouly not disable preemption, but it should still trigger the might_sleep() check when a blocking function is called from within a rcu read side critical section. Thanks, tglx