Subject: block: Shorten interrupt disabled regions From: Thomas Gleixner Date: Wed, 22 Jun 2011 19:47:02 +0200 Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.16/older/patches-4.16.8-rt3.tar.xz Commit 9c40cef2b799 ("sched: Move blk_schedule_flush_plug() out of __schedule()") moved the blk_schedule_flush_plug() call out of the interrupt/preempt disabled region in the scheduler. This allows to replace local_irq_save/restore(flags) by local_irq_disable/enable() in blk_flush_plug_list(). But it makes more sense to disable interrupts explicitly when the request queue is locked end reenable them when the request to is unlocked. This shortens the interrupt disabled section which is important when the plug list contains requests for more than one queue. The comment which claims that disabling interrupts around the loop is misleading as the called functions can reenable interrupts unconditionally anyway and obfuscates the scope badly: local_irq_save(flags); spin_lock(q->queue_lock); ... queue_unplugged(q...); scsi_request_fn(); spin_unlock_irq(q->queue_lock); -------------------^^^ ???? spin_lock_irq(q->queue_lock); spin_unlock(q->queue_lock); local_irq_restore(flags); Aside of that the detached interrupt disabling is a constant pain for PREEMPT_RT as it requires patching and special casing when RT is enabled while with the spin_*_irq() variants this happens automatically. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Tejun Heo Cc: Jens Axboe Cc: Linus Torvalds Link: http://lkml.kernel.org/r/20110622174919.025446432@linutronix.de --- block/blk-core.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) --- a/block/blk-core.c +++ b/block/blk-core.c @@ -3520,7 +3520,7 @@ static void queue_unplugged(struct reque blk_run_queue_async(q); else __blk_run_queue(q); - spin_unlock(q->queue_lock); + spin_unlock_irq(q->queue_lock); } static void flush_plug_callbacks(struct blk_plug *plug, bool from_schedule) @@ -3568,7 +3568,6 @@ EXPORT_SYMBOL(blk_check_plugged); void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule) { struct request_queue *q; - unsigned long flags; struct request *rq; LIST_HEAD(list); unsigned int depth; @@ -3588,11 +3587,6 @@ void blk_flush_plug_list(struct blk_plug q = NULL; depth = 0; - /* - * Save and disable interrupts here, to avoid doing it for every - * queue lock we have to take. - */ - local_irq_save(flags); while (!list_empty(&list)) { rq = list_entry_rq(list.next); list_del_init(&rq->queuelist); @@ -3605,7 +3599,7 @@ void blk_flush_plug_list(struct blk_plug queue_unplugged(q, depth, from_schedule); q = rq->q; depth = 0; - spin_lock(q->queue_lock); + spin_lock_irq(q->queue_lock); } /* @@ -3632,8 +3626,6 @@ void blk_flush_plug_list(struct blk_plug */ if (q) queue_unplugged(q, depth, from_schedule); - - local_irq_restore(flags); } void blk_finish_plug(struct blk_plug *plug)