X-Git-Url: http://git.osdn.net/view?a=blobdiff_plain;f=block%2Fblk-core.c;h=1ccec27d20c38d8d2613893092e67292d3baae0f;hb=7c2614bf7a1fc0da0743129e5b60af82f34cde55;hp=c78042975737401cac2dd937c558edfc49fc780c;hpb=0fe4e2d5cd931ad2ff99d61cfdd5c6dc0c3ec60b;p=uclinux-h8%2Flinux.git

diff --git a/block/blk-core.c b/block/blk-core.c
index c78042975737..1ccec27d20c3 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -661,7 +661,6 @@ no_merge:
  * blk_attempt_plug_merge - try to merge with %current's plugged list
  * @q: request_queue new bio is being queued at
  * @bio: new bio being queued
- * @request_count: out parameter for number of traversed plugged requests
  * @same_queue_rq: pointer to &struct request that gets filled in when
  * another request associated with @q is found on the plug list
  * (optional, may be %NULL)
@@ -1084,7 +1083,18 @@ blk_qc_t generic_make_request(struct bio *bio)
 			/* Create a fresh bio_list for all subordinate requests */
 			bio_list_on_stack[1] = bio_list_on_stack[0];
 			bio_list_init(&bio_list_on_stack[0]);
+
+			/*
+			 * Since we're recursing into make_request here, ensure
+			 * that we mark this bio as already having entered the queue.
+			 * If not, and the queue is going away, we can get stuck
+			 * forever on waiting for the queue reference to drop. But
+			 * that will never happen, as we're already holding a
+			 * reference to it.
+			 */
+			bio_set_flag(bio, BIO_QUEUE_ENTERED);
 			ret = q->make_request_fn(q, bio);
+			bio_clear_flag(bio, BIO_QUEUE_ENTERED);
 
 			/* sort new bios into those for a lower level
 			 * and those for the same level
@@ -1683,6 +1693,15 @@ EXPORT_SYMBOL(kblockd_mod_delayed_work_on);
  * @plug:	The &struct blk_plug that needs to be initialized
  *
  * Description:
+ *   blk_start_plug() indicates to the block layer an intent by the caller
+ *   to submit multiple I/O requests in a batch.  The block layer may use
+ *   this hint to defer submitting I/Os from the caller until blk_finish_plug()
+ *   is called.  However, the block layer may choose to submit requests
+ *   before a call to blk_finish_plug() if the number of queued I/Os
+ *   exceeds %BLK_MAX_REQUEST_COUNT, or if the size of the I/O is larger than
+ *   %BLK_PLUG_FLUSH_SIZE.  The queued I/Os may also be submitted early if
+ *   the task schedules (see below).
+ *
  *   Tracking blk_plug inside the task_struct will help with auto-flushing the
  *   pending I/O should the task end up blocking between blk_start_plug() and
  *   blk_finish_plug(). This is important from a performance perspective, but
@@ -1765,6 +1784,16 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 		blk_mq_flush_plug_list(plug, from_schedule);
 }
 
+/**
+ * blk_finish_plug - mark the end of a batch of submitted I/O
+ * @plug:	The &struct blk_plug passed to blk_start_plug()
+ *
+ * Description:
+ * Indicate that a batch of I/O submissions is complete.  This function
+ * must be paired with an initial call to blk_start_plug().  The intent
+ * is to allow the block layer to optimize I/O submission.  See the
+ * documentation for blk_start_plug() for more information.
+ */
 void blk_finish_plug(struct blk_plug *plug)
 {
 	if (plug != current->plug)