block: make queue flags non-atomic

We can save some atomic ops in the IO path, if we clearly define
the rules of how to modify the queue flags.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

13 files changed, 102 insertions, 49 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index e447799256d6..d2f23ec5ebfa 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -198,7 +198,8 @@ void blk_plug_device(struct request_queue *q)
         if (blk_queue_stopped(q))
                 return;
 
-        if (!test_and_set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags)) {
+        if (!test_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags)) {
+                __set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags);
                 mod_timer(&q->unplug_timer, jiffies + q->unplug_delay);
                 blk_add_trace_generic(q, NULL, 0, BLK_TA_PLUG);
         }
@@ -213,9 +214,10 @@ int blk_remove_plug(struct request_queue *q)
 {
         WARN_ON(!irqs_disabled());
 
-        if (!test_and_clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
+        if (!test_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
                 return 0;
 
+        queue_flag_clear(QUEUE_FLAG_PLUGGED, q);
         del_timer(&q->unplug_timer);
         return 1;
 }
@@ -311,15 +313,16 @@ void blk_start_queue(struct request_queue *q)
 {
         WARN_ON(!irqs_disabled());
 
-        clear_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
+        queue_flag_clear(QUEUE_FLAG_STOPPED, q);
 
         /*
          * one level of recursion is ok and is much faster than kicking
          * the unplug handling
          */
-        if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
+        if (!test_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
+                queue_flag_set(QUEUE_FLAG_REENTER, q);
                 q->request_fn(q);
-                clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags);
+                queue_flag_clear(QUEUE_FLAG_REENTER, q);
         } else {
                 blk_plug_device(q);
                 kblockd_schedule_work(&q->unplug_work);
@@ -344,7 +347,7 @@ EXPORT_SYMBOL(blk_start_queue);
 void blk_stop_queue(struct request_queue *q)
 {
         blk_remove_plug(q);
-        set_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
+        queue_flag_set(QUEUE_FLAG_STOPPED, q);
 }
 EXPORT_SYMBOL(blk_stop_queue);
 
@@ -373,11 +376,8 @@ EXPORT_SYMBOL(blk_sync_queue);
  * blk_run_queue - run a single device queue
  * @q:  The queue to run
  */
-void blk_run_queue(struct request_queue *q)
+void __blk_run_queue(struct request_queue *q)
 {
-        unsigned long flags;
-
-        spin_lock_irqsave(q->queue_lock, flags);
         blk_remove_plug(q);
 
         /*
@@ -385,15 +385,28 @@ void blk_run_queue(struct request_queue *q)
          * handling reinvoke the handler shortly if we already got there.
          */
         if (!elv_queue_empty(q)) {
-                if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
+                if (!test_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
+                        queue_flag_set(QUEUE_FLAG_REENTER, q);
                         q->request_fn(q);
-                        clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags);
+                        queue_flag_clear(QUEUE_FLAG_REENTER, q);
                 } else {
                         blk_plug_device(q);
                         kblockd_schedule_work(&q->unplug_work);
                 }
         }
+}
+EXPORT_SYMBOL(__blk_run_queue);
 
+/**
+ * blk_run_queue - run a single device queue
+ * @q: The queue to run
+ */
+void blk_run_queue(struct request_queue *q)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(q->queue_lock, flags);
+        __blk_run_queue(q);
         spin_unlock_irqrestore(q->queue_lock, flags);
 }
 EXPORT_SYMBOL(blk_run_queue);
@@ -406,7 +419,7 @@ void blk_put_queue(struct request_queue *q)
 void blk_cleanup_queue(struct request_queue *q)
 {
         mutex_lock(&q->sysfs_lock);
-        set_bit(QUEUE_FLAG_DEAD, &q->queue_flags);
+        queue_flag_set_unlocked(QUEUE_FLAG_DEAD, q);
         mutex_unlock(&q->sysfs_lock);
 
         if (q->elevator)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index b5c5c4a9e3f0..73b23562af20 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -55,7 +55,7 @@ void blk_recalc_rq_segments(struct request *rq)
         if (!rq->bio)
                 return;
 
-        cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+        cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
         hw_seg_size = seg_size = 0;
         phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
         rq_for_each_segment(bv, rq, iter) {
@@ -128,7 +128,7 @@ EXPORT_SYMBOL(blk_recount_segments);
 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
                                    struct bio *nxt)
 {
-        if (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER)))
+        if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
                 return 0;
 
         if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
@@ -175,7 +175,7 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
         int nsegs, cluster;
 
         nsegs = 0;
-        cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+        cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
 
         /*
          * for each bio in rq
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 77b51dc37a3c..6089384ab064 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -287,7 +287,7 @@ void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
         t->max_segment_size = min(t->max_segment_size, b->max_segment_size);
         t->hardsect_size = max(t->hardsect_size, b->hardsect_size);
         if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
-                clear_bit(QUEUE_FLAG_CLUSTER, &t->queue_flags);
+                queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
 }
 EXPORT_SYMBOL(blk_queue_stack_limits);
 
diff --git a/block/blk-tag.c b/block/blk-tag.c
index 4780a46ce234..e176ddbe599e 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -70,7 +70,7 @@ void __blk_queue_free_tags(struct request_queue *q)
         __blk_free_tags(bqt);
 
         q->queue_tags = NULL;
-        q->queue_flags &= ~(1 << QUEUE_FLAG_QUEUED);
+        queue_flag_clear(QUEUE_FLAG_QUEUED, q);
 }
 
 /**
@@ -98,7 +98,7 @@ EXPORT_SYMBOL(blk_free_tags);
  **/
 void blk_queue_free_tags(struct request_queue *q)
 {
-        clear_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+        queue_flag_clear(QUEUE_FLAG_QUEUED, q);
 }
 EXPORT_SYMBOL(blk_queue_free_tags);
 
@@ -188,7 +188,7 @@ int blk_queue_init_tags(struct request_queue *q, int depth,
                 rc = blk_queue_resize_tags(q, depth);
                 if (rc)
                         return rc;
-                set_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+                queue_flag_set(QUEUE_FLAG_QUEUED, q);
                 return 0;
         } else
                 atomic_inc(&tags->refcnt);
@@ -197,7 +197,7 @@ int blk_queue_init_tags(struct request_queue *q, int depth,
          * assign it, all done
          */
         q->queue_tags = tags;
-        q->queue_flags |= (1 << QUEUE_FLAG_QUEUED);
+        queue_flag_set(QUEUE_FLAG_QUEUED, q);
         INIT_LIST_HEAD(&q->tag_busy_list);
         return 0;
 fail:
diff --git a/block/elevator.c b/block/elevator.c
index 88318c383608..e8a90fe23424 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1070,7 +1070,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
          */
         spin_lock_irq(q->queue_lock);
 
-        set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
 
         elv_drain_elevator(q);
 
@@ -1104,7 +1104,10 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
          * finally exit old elevator and turn off BYPASS.
          */
         elevator_exit(old_elevator);
-        clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+        spin_lock_irq(q->queue_lock);
+        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+        spin_unlock_irq(q->queue_lock);
+
         return 1;
 
 fail_register:
@@ -1115,7 +1118,11 @@ fail_register:
         elevator_exit(e);
         q->elevator = old_elevator;
         elv_register_queue(q);
-        clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+
+        spin_lock_irq(q->queue_lock);
+        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+        spin_unlock_irq(q->queue_lock);
+
         return 0;
 }
 
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index f7f163557aa0..d3a25b027ff9 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -546,7 +546,7 @@ static void loop_unplug(struct request_queue *q)
 {
         struct loop_device *lo = q->queuedata;
 
-        clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags);
+        queue_flag_clear_unlocked(QUEUE_FLAG_PLUGGED, q);
         blk_run_address_space(lo->lo_backing_file->f_mapping);
 }
 
diff --git a/drivers/block/ub.c b/drivers/block/ub.c
index 27bfe72aab59..e322cce8c12d 100644
--- a/drivers/block/ub.c
+++ b/drivers/block/ub.c
@@ -2399,7 +2399,7 @@ static void ub_disconnect(struct usb_interface *intf)
                 del_gendisk(lun->disk);
                 /*
                  * I wish I could do:
-                 *    set_bit(QUEUE_FLAG_DEAD, &q->queue_flags);
+                 *    queue_flag_set(QUEUE_FLAG_DEAD, q);
                  * As it is, we rely on our internal poisoning and let
                  * the upper levels to spin furiously failing all the I/O.
                  */
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 51be53344214..73326e7c54bf 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -873,10 +873,13 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q)
         q->max_hw_sectors = t->limits.max_hw_sectors;
         q->seg_boundary_mask = t->limits.seg_boundary_mask;
         q->bounce_pfn = t->limits.bounce_pfn;
+        /* XXX: the below will probably go bug. must ensure there can be no
+         * concurrency on queue_flags, and use the unlocked versions...
+         */
         if (t->limits.no_cluster)
-                q->queue_flags &= ~(1 << QUEUE_FLAG_CLUSTER);
+                queue_flag_clear(QUEUE_FLAG_CLUSTER, q);
         else
-                q->queue_flags |= (1 << QUEUE_FLAG_CLUSTER);
+                queue_flag_set(QUEUE_FLAG_CLUSTER, q);
 
 }
 
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 87620b705bee..acd716b657b8 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -282,7 +282,8 @@ static mddev_t * mddev_find(dev_t unit)
                 kfree(new);
                 return NULL;
         }
-        set_bit(QUEUE_FLAG_CLUSTER, &new->queue->queue_flags);
+        /* Can be unlocked because the queue is new: no concurrency */
+        queue_flag_set_unlocked(QUEUE_FLAG_CLUSTER, new->queue);
 
         blk_queue_make_request(new->queue, md_fail_request);
 
diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 07103c399fe0..f6600bfb5bde 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -1773,7 +1773,7 @@ static int scsi_debug_slave_alloc(struct scsi_device *sdp)
         if (SCSI_DEBUG_OPT_NOISE & scsi_debug_opts)
                 printk(KERN_INFO "scsi_debug: slave_alloc <%u %u %u %u>\n",
                        sdp->host->host_no, sdp->channel, sdp->id, sdp->lun);
-        set_bit(QUEUE_FLAG_BIDI, &sdp->request_queue->queue_flags);
+        queue_flag_set_unlocked(QUEUE_FLAG_BIDI, sdp->request_queue);
         return 0;
 }
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 67f412bb4974..d545ad1cf47a 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -536,6 +536,9 @@ static void scsi_run_queue(struct request_queue *q)
                !shost->host_blocked && !shost->host_self_blocked &&
                 !((shost->can_queue > 0) &&
                   (shost->host_busy >= shost->can_queue))) {
+
+                int flagset;
+
                 /*
                  * As long as shost is accepting commands and we have
                  * starved queues, call blk_run_queue. scsi_request_fn
@@ -549,19 +552,20 @@ static void scsi_run_queue(struct request_queue *q)
                 sdev = list_entry(shost->starved_list.next,
                                           struct scsi_device, starved_entry);
                 list_del_init(&sdev->starved_entry);
-                spin_unlock_irqrestore(shost->host_lock, flags);
-
+                spin_unlock(shost->host_lock);
+
+                spin_lock(sdev->request_queue->queue_lock);
+                flagset = test_bit(QUEUE_FLAG_REENTER, &q->queue_flags) &&
+                                !test_bit(QUEUE_FLAG_REENTER,
+                                        &sdev->request_queue->queue_flags);
+                if (flagset)
+                        queue_flag_set(QUEUE_FLAG_REENTER, sdev->request_queue);
+                __blk_run_queue(sdev->request_queue);
+                if (flagset)
+                        queue_flag_clear(QUEUE_FLAG_REENTER, sdev->request_queue);
+                spin_unlock(sdev->request_queue->queue_lock);
 
-                if (test_bit(QUEUE_FLAG_REENTER, &q->queue_flags) &&
-                    !test_and_set_bit(QUEUE_FLAG_REENTER,
-                                      &sdev->request_queue->queue_flags)) {
-                        blk_run_queue(sdev->request_queue);
-                        clear_bit(QUEUE_FLAG_REENTER,
-                                  &sdev->request_queue->queue_flags);
-                } else
-                        blk_run_queue(sdev->request_queue);
-
-                spin_lock_irqsave(shost->host_lock, flags);
+                spin_lock(shost->host_lock);
                 if (unlikely(!list_empty(&sdev->starved_entry)))
                         /*
                          * sdev lost a race, and was put back on the
@@ -1585,8 +1589,9 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
 
         blk_queue_max_segment_size(q, dma_get_max_seg_size(dev));
 
+        /* New queue, no concurrency on queue_flags */
         if (!shost->use_clustering)
-                clear_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
+                queue_flag_clear_unlocked(QUEUE_FLAG_CLUSTER, q);
 
         /*
          * set a reasonable default alignment on word boundaries: the
diff --git a/drivers/scsi/scsi_transport_sas.c b/drivers/scsi/scsi_transport_sas.c
index 7899e3dda9bf..f4461d35ffb9 100644
--- a/drivers/scsi/scsi_transport_sas.c
+++ b/drivers/scsi/scsi_transport_sas.c
@@ -248,8 +248,7 @@ static int sas_bsg_initialize(struct Scsi_Host *shost, struct sas_rphy *rphy)
         else
                 q->queuedata = shost;
 
-        set_bit(QUEUE_FLAG_BIDI, &q->queue_flags);
-
+        queue_flag_set_unlocked(QUEUE_FLAG_BIDI, q);
         return 0;
 }
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c5065e3d2ca9..8ca481cd7d73 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -408,6 +408,30 @@ struct request_queue
 #define QUEUE_FLAG_ELVSWITCH    8       /* don't use elevator, just do FIFO */
 #define QUEUE_FLAG_BIDI         9       /* queue supports bidi requests */
 
+static inline void queue_flag_set_unlocked(unsigned int flag,
+                                           struct request_queue *q)
+{
+        __set_bit(flag, &q->queue_flags);
+}
+
+static inline void queue_flag_set(unsigned int flag, struct request_queue *q)
+{
+        WARN_ON_ONCE(!spin_is_locked(q->queue_lock));
+        __set_bit(flag, &q->queue_flags);
+}
+
+static inline void queue_flag_clear_unlocked(unsigned int flag,
+                                             struct request_queue *q)
+{
+        __clear_bit(flag, &q->queue_flags);
+}
+
+static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
+{
+        WARN_ON_ONCE(!spin_is_locked(q->queue_lock));
+        __clear_bit(flag, &q->queue_flags);
+}
+
 enum {
         /*
          * Hardbarrier is supported with one of the following methods.
@@ -496,17 +520,17 @@ static inline int blk_queue_full(struct request_queue *q, int rw)
 static inline void blk_set_queue_full(struct request_queue *q, int rw)
 {
         if (rw == READ)
-                set_bit(QUEUE_FLAG_READFULL, &q->queue_flags);
+                queue_flag_set(QUEUE_FLAG_READFULL, q);
         else
-                set_bit(QUEUE_FLAG_WRITEFULL, &q->queue_flags);
+                queue_flag_set(QUEUE_FLAG_WRITEFULL, q);
 }
 
 static inline void blk_clear_queue_full(struct request_queue *q, int rw)
 {
         if (rw == READ)
-                clear_bit(QUEUE_FLAG_READFULL, &q->queue_flags);
+                queue_flag_clear(QUEUE_FLAG_READFULL, q);
         else
-                clear_bit(QUEUE_FLAG_WRITEFULL, &q->queue_flags);
+                queue_flag_clear(QUEUE_FLAG_WRITEFULL, q);
 }
 
 
@@ -626,6 +650,7 @@ extern void blk_start_queue(struct request_queue *q);
 extern void blk_stop_queue(struct request_queue *q);
 extern void blk_sync_queue(struct request_queue *q);
 extern void __blk_stop_queue(struct request_queue *q);
+extern void __blk_run_queue(struct request_queue *);
 extern void blk_run_queue(struct request_queue *);
 extern void blk_start_queueing(struct request_queue *);
 extern int blk_rq_map_user(struct request_queue *, struct request *, void __user *, unsigned long);