From f1a71391ee4e45fec5f6624aa8b1a04f4da89826 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 22 Jun 2011 19:47:02 +0200 Subject: [PATCH 048/365] block: Shorten interrupt disabled regions Moving the blk_sched_flush_plug() call out of the interrupt/preempt disabled region in the scheduler allows us to replace local_irq_save/restore(flags) by local_irq_disable/enable() in blk_flush_plug(). Now instead of doing this we disable interrupts explicitely when we lock the request_queue and reenable them when we drop the lock. That allows interrupts to be handled when the plug list contains requests for more than one queue. Aside of that this change makes the scope of the irq disabled region more obvious. The current code confused the hell out of me when looking at: local_irq_save(flags); spin_lock(q->queue_lock); ... queue_unplugged(q...); scsi_request_fn(); spin_unlock(q->queue_lock); spin_lock(shost->host_lock); spin_unlock_irq(shost->host_lock); -------------------^^^ ???? spin_lock_irq(q->queue_lock); spin_unlock(q->lock); local_irq_restore(flags); Also add a comment to __blk_run_queue() documenting that q->request_fn() can drop q->queue_lock and reenable interrupts, but must return with q->queue_lock held and interrupts disabled. 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(-) diff --git a/block/blk-core.c b/block/blk-core.c index 27621cd16993..9fa645750c1b 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -3205,7 +3205,7 @@ static void queue_unplugged(struct request_queue *q, unsigned int depth, 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) @@ -3253,7 +3253,6 @@ 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; @@ -3273,11 +3272,6 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule) 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); @@ -3290,7 +3284,7 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule) queue_unplugged(q, depth, from_schedule); q = rq->q; depth = 0; - spin_lock(q->queue_lock); + spin_lock_irq(q->queue_lock); } /* @@ -3317,8 +3311,6 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule) */ if (q) queue_unplugged(q, depth, from_schedule); - - local_irq_restore(flags); } void blk_finish_plug(struct blk_plug *plug) -- 2.28.0