1 files changed, 71 insertions, 80 deletions

diff --git a/drivers/block/ll_rw_blk.c b/drivers/block/ll_rw_blk.c
index 234fdcfbdf01..692a5fced76e 100644
--- a/drivers/block/ll_rw_blk.c
+++ b/drivers/block/ll_rw_blk.c
@@ -1867,19 +1867,20 @@ static void freed_request(request_queue_t *q, int rw)
 
 #define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
 /*
- * Get a free request, queue_lock must not be held
+ * Get a free request, queue_lock must be held.
+ * Returns NULL on failure, with queue_lock held.
+ * Returns !NULL on success, with queue_lock *not held*.
  */
 static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
                                    int gfp_mask)
 {
         struct request *rq = NULL;
         struct request_list *rl = &q->rq;
-        struct io_context *ioc = get_io_context(gfp_mask);
+        struct io_context *ioc = current_io_context(GFP_ATOMIC);
 
         if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)))
                 goto out;
 
-        spin_lock_irq(q->queue_lock);
         if (rl->count[rw]+1 >= q->nr_requests) {
                 /*
                  * The queue will fill after this allocation, so set it as
@@ -1907,11 +1908,18 @@ static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
                  * The queue is full and the allocating process is not a
                  * "batcher", and not exempted by the IO scheduler
                  */
-                spin_unlock_irq(q->queue_lock);
                 goto out;
         }
 
 get_rq:
+        /*
+         * Only allow batching queuers to allocate up to 50% over the defined
+         * limit of requests, otherwise we could have thousands of requests
+         * allocated with any setting of ->nr_requests
+         */
+        if (rl->count[rw] >= (3 * q->nr_requests / 2))
+                goto out;
+
         rl->count[rw]++;
         rl->starved[rw] = 0;
         if (rl->count[rw] >= queue_congestion_on_threshold(q))
@@ -1941,7 +1949,6 @@ rq_starved:
                 if (unlikely(rl->count[rw] == 0))
                         rl->starved[rw] = 1;
 
-                spin_unlock_irq(q->queue_lock);
                 goto out;
         }
 
@@ -1951,21 +1958,23 @@ rq_starved:
         rq_init(q, rq);
         rq->rl = rl;
 out:
-        put_io_context(ioc);
         return rq;
 }
 
 /*
  * No available requests for this queue, unplug the device and wait for some
  * requests to become available.
+ *
+ * Called with q->queue_lock held, and returns with it unlocked.
  */
 static struct request *get_request_wait(request_queue_t *q, int rw,
                                         struct bio *bio)
 {
-        DEFINE_WAIT(wait);
         struct request *rq;
 
-        do {
+        rq = get_request(q, rw, bio, GFP_NOIO);
+        while (!rq) {
+                DEFINE_WAIT(wait);
                 struct request_list *rl = &q->rq;
 
                 prepare_to_wait_exclusive(&rl->wait[rw], &wait,
@@ -1976,7 +1985,8 @@ static struct request *get_request_wait(request_queue_t *q, int rw,
                 if (!rq) {
                         struct io_context *ioc;
 
-                        generic_unplug_device(q);
+                        __generic_unplug_device(q);
+                        spin_unlock_irq(q->queue_lock);
                         io_schedule();
 
                         /*
@@ -1985,12 +1995,13 @@ static struct request *get_request_wait(request_queue_t *q, int rw,
                          * up to a big batch of them for a small period time.
                          * See ioc_batching, ioc_set_batching
                          */
-                        ioc = get_io_context(GFP_NOIO);
+                        ioc = current_io_context(GFP_NOIO);
                         ioc_set_batching(q, ioc);
-                        put_io_context(ioc);
+
+                        spin_lock_irq(q->queue_lock);
                 }
                 finish_wait(&rl->wait[rw], &wait);
-        } while (!rq);
+        }
 
         return rq;
 }
@@ -2001,14 +2012,18 @@ struct request *blk_get_request(request_queue_t *q, int rw, int gfp_mask)
 
         BUG_ON(rw != READ && rw != WRITE);
 
-        if (gfp_mask & __GFP_WAIT)
+        spin_lock_irq(q->queue_lock);
+        if (gfp_mask & __GFP_WAIT) {
                 rq = get_request_wait(q, rw, NULL);
-        else
+        } else {
                 rq = get_request(q, rw, NULL, gfp_mask);
+                if (!rq)
+                        spin_unlock_irq(q->queue_lock);
+        }
+        /* q->queue_lock is unlocked at this point */
 
         return rq;
 }
-
 EXPORT_SYMBOL(blk_get_request);
 
 /**
@@ -2512,7 +2527,7 @@ EXPORT_SYMBOL(blk_attempt_remerge);
 
 static int __make_request(request_queue_t *q, struct bio *bio)
 {
-        struct request *req, *freereq = NULL;
+        struct request *req;
         int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, err, sync;
         unsigned short prio;
         sector_t sector;
@@ -2540,14 +2555,9 @@ static int __make_request(request_queue_t *q, struct bio *bio)
                 goto end_io;
         }
 
-again:
         spin_lock_irq(q->queue_lock);
 
-        if (elv_queue_empty(q)) {
-                blk_plug_device(q);
-                goto get_rq;
-        }
-        if (barrier)
+        if (unlikely(barrier) || elv_queue_empty(q))
                 goto get_rq;
 
         el_ret = elv_merge(q, &req, bio);
@@ -2592,40 +2602,24 @@ again:
                                 elv_merged_request(q, req);
                         goto out;
 
-                /*
-                 * elevator says don't/can't merge. get new request
-                 */
-                case ELEVATOR_NO_MERGE:
-                        break;
-
+                /* ELV_NO_MERGE: elevator says don't/can't merge. */
                 default:
-                        printk("elevator returned crap (%d)\n", el_ret);
-                        BUG();
+                        ;
         }
 
+get_rq:
         /*
-         * Grab a free request from the freelist - if that is empty, check
-         * if we are doing read ahead and abort instead of blocking for
-         * a free slot.
+         * Grab a free request. This is might sleep but can not fail.
+         * Returns with the queue unlocked.
+         */
+        req = get_request_wait(q, rw, bio);
+
+        /*
+         * After dropping the lock and possibly sleeping here, our request
+         * may now be mergeable after it had proven unmergeable (above).
+         * We don't worry about that case for efficiency. It won't happen
+         * often, and the elevators are able to handle it.
          */
-get_rq:
-        if (freereq) {
-                req = freereq;
-                freereq = NULL;
-        } else {
-                spin_unlock_irq(q->queue_lock);
-                if ((freereq = get_request(q, rw, bio, GFP_ATOMIC)) == NULL) {
-                        /*
-                         * READA bit set
-                         */
-                        err = -EWOULDBLOCK;
-                        if (bio_rw_ahead(bio))
-                                goto end_io;
-        
-                        freereq = get_request_wait(q, rw, bio);
-                }
-                goto again;
-        }
 
         req->flags |= REQ_CMD;
 
@@ -2654,10 +2648,11 @@ get_rq:
         req->rq_disk = bio->bi_bdev->bd_disk;
         req->start_time = jiffies;
 
+        spin_lock_irq(q->queue_lock);
+        if (elv_queue_empty(q))
+                blk_plug_device(q);
         add_request(q, req);
 out:
-        if (freereq)
-                __blk_put_request(q, freereq);
         if (sync)
                 __generic_unplug_device(q);
 
@@ -3284,24 +3279,20 @@ void exit_io_context(void)
 
 /*
  * If the current task has no IO context then create one and initialise it.
- * If it does have a context, take a ref on it.
+ * Otherwise, return its existing IO context.
  *
- * This is always called in the context of the task which submitted the I/O.
- * But weird things happen, so we disable local interrupts to ensure exclusive
- * access to *current.
+ * This returned IO context doesn't have a specifically elevated refcount,
+ * but since the current task itself holds a reference, the context can be
+ * used in general code, so long as it stays within `current` context.
  */
-struct io_context *get_io_context(int gfp_flags)
+struct io_context *current_io_context(int gfp_flags)
 {
         struct task_struct *tsk = current;
-        unsigned long flags;
         struct io_context *ret;
 
-        local_irq_save(flags);
         ret = tsk->io_context;
-        if (ret)
-                goto out;
-
-        local_irq_restore(flags);
+        if (likely(ret))
+                return ret;
 
         ret = kmem_cache_alloc(iocontext_cachep, gfp_flags);
         if (ret) {
@@ -3312,25 +3303,25 @@ struct io_context *get_io_context(int gfp_flags)
                 ret->nr_batch_requests = 0; /* because this is 0 */
                 ret->aic = NULL;
                 ret->cic = NULL;
+                tsk->io_context = ret;
+        }
 
-                local_irq_save(flags);
-
-                /*
-                 * very unlikely, someone raced with us in setting up the task
-                 * io context. free new context and just grab a reference.
-                 */
-                if (!tsk->io_context)
-                        tsk->io_context = ret;
-                else {
-                        kmem_cache_free(iocontext_cachep, ret);
-                        ret = tsk->io_context;
-                }
+        return ret;
+}
+EXPORT_SYMBOL(current_io_context);
 
-out:
+/*
+ * If the current task has no IO context then create one and initialise it.
+ * If it does have a context, take a ref on it.
+ *
+ * This is always called in the context of the task which submitted the I/O.
+ */
+struct io_context *get_io_context(int gfp_flags)
+{
+        struct io_context *ret;
+        ret = current_io_context(gfp_flags);
+        if (likely(ret))
                 atomic_inc(&ret->refcount);
-                local_irq_restore(flags);
-        }
-
         return ret;
 }
 EXPORT_SYMBOL(get_io_context);