Hello, On Mon, Mar 19, 2018 at 03:16:07PM +0000, Bart Van Assche wrote: > As explained in the comment in scsi_device_quiesce(), the effect of > blk_set_preempt_only() must be visible for percpu_ref_tryget() calls that > occur after the queue unfreeze triggered by scsi_device_quiesce(). Hence the > RCU read lock calls in blk_queue_enter(). Since these RCU read lock calls > surround a function call that uses rcu_read_lock_sched(), namely > percpu_ref_tryget_live(), we have to use sched-RCU in both blk_queue_enter() > and scsi_device_quiesce(). Let's please not depend on rcu_read_lock_sched() in percpu_ref_tryget_live(). That's an implementation detail. If the code needs RCU based synchronization, it should perform them explicitly. Thanks. -- tejun
