5 files changed, 45 insertions, 19 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 3c8121072507..78b7b0cb7216 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2662,17 +2662,23 @@ static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
         return !(rqa->q <= rqb->q);
 }
 
+/*
+ * If 'from_schedule' is true, then postpone the dispatch of requests
+ * until a safe kblockd context. We due this to avoid accidental big
+ * additional stack usage in driver dispatch, in places where the originally
+ * plugger did not intend it.
+ */
 static void queue_unplugged(struct request_queue *q, unsigned int depth,
-                            bool force_kblockd)
+                            bool from_schedule)
 {
-        trace_block_unplug_io(q, depth);
-        __blk_run_queue(q, force_kblockd);
+        trace_block_unplug(q, depth, !from_schedule);
+        __blk_run_queue(q, from_schedule);
 
         if (q->unplugged_fn)
                 q->unplugged_fn(q);
 }
 
-void blk_flush_plug_list(struct blk_plug *plug, bool force_kblockd)
+void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 {
         struct request_queue *q;
         unsigned long flags;
@@ -2707,7 +2713,7 @@ void blk_flush_plug_list(struct blk_plug *plug, bool force_kblockd)
                 BUG_ON(!rq->q);
                 if (rq->q != q) {
                         if (q) {
-                                queue_unplugged(q, depth, force_kblockd);
+                                queue_unplugged(q, depth, from_schedule);
                                 spin_unlock(q->queue_lock);
                         }
                         q = rq->q;
@@ -2728,7 +2734,7 @@ void blk_flush_plug_list(struct blk_plug *plug, bool force_kblockd)
         }
 
         if (q) {
-                queue_unplugged(q, depth, force_kblockd);
+                queue_unplugged(q, depth, from_schedule);
                 spin_unlock(q->queue_lock);
         }
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1c76506fcf11..ec0357d8c4a5 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -872,6 +872,14 @@ static inline void blk_flush_plug(struct task_struct *tsk)
         struct blk_plug *plug = tsk->plug;
 
         if (plug)
+                blk_flush_plug_list(plug, false);
+}
+
+static inline void blk_schedule_flush_plug(struct task_struct *tsk)
+{
+        struct blk_plug *plug = tsk->plug;
+
+        if (plug)
                 blk_flush_plug_list(plug, true);
 }
 
@@ -1317,6 +1325,11 @@ static inline void blk_flush_plug(struct task_struct *task)
 {
 }
 
+static inline void blk_schedule_flush_plug(struct task_struct *task)
+{
+}
+
+
 static inline bool blk_needs_flush_plug(struct task_struct *tsk)
 {
         return false;
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 006e60b58306..bf366547da25 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -401,9 +401,9 @@ TRACE_EVENT(block_plug,
 
 DECLARE_EVENT_CLASS(block_unplug,
 
-        TP_PROTO(struct request_queue *q, unsigned int depth),
+        TP_PROTO(struct request_queue *q, unsigned int depth, bool explicit),
 
-        TP_ARGS(q, depth),
+        TP_ARGS(q, depth, explicit),
 
         TP_STRUCT__entry(
                 __field( int,           nr_rq                   )
@@ -419,18 +419,19 @@ DECLARE_EVENT_CLASS(block_unplug,
 );
 
 /**
- * block_unplug_io - release of operations requests in request queue
+ * block_unplug - release of operations requests in request queue
  * @q: request queue to unplug
  * @depth: number of requests just added to the queue
+ * @explicit: whether this was an explicit unplug, or one from schedule()
  *
  * Unplug request queue @q because device driver is scheduled to work
  * on elements in the request queue.
  */
-DEFINE_EVENT(block_unplug, block_unplug_io,
+DEFINE_EVENT(block_unplug, block_unplug,
 
-        TP_PROTO(struct request_queue *q, unsigned int depth),
+        TP_PROTO(struct request_queue *q, unsigned int depth, bool explicit),
 
-        TP_ARGS(q, depth)
+        TP_ARGS(q, depth, explicit)
 );
 
 /**
diff --git a/kernel/sched.c b/kernel/sched.c
index a187c3fe027b..312f8b95c2d4 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4118,7 +4118,7 @@ need_resched:
                          */
                         if (blk_needs_flush_plug(prev)) {
                                 raw_spin_unlock(&rq->lock);
-                                blk_flush_plug(prev);
+                                blk_schedule_flush_plug(prev);
                                 raw_spin_lock(&rq->lock);
                         }
                 }
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 3e3970d53d14..6957aa298dfa 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -850,16 +850,21 @@ static void blk_add_trace_plug(void *ignore, struct request_queue *q)
                 __blk_add_trace(bt, 0, 0, 0, BLK_TA_PLUG, 0, 0, NULL);
 }
 
-static void blk_add_trace_unplug_io(void *ignore, struct request_queue *q,
-                                    unsigned int depth)
+static void blk_add_trace_unplug(void *ignore, struct request_queue *q,
+                                    unsigned int depth, bool explicit)
 {
         struct blk_trace *bt = q->blk_trace;
 
         if (bt) {
                 __be64 rpdu = cpu_to_be64(depth);
+                u32 what;
 
-                __blk_add_trace(bt, 0, 0, 0, BLK_TA_UNPLUG_IO, 0,
-                                sizeof(rpdu), &rpdu);
+                if (explicit)
+                        what = BLK_TA_UNPLUG_IO;
+                else
+                        what = BLK_TA_UNPLUG_TIMER;
+
+                __blk_add_trace(bt, 0, 0, 0, what, 0, sizeof(rpdu), &rpdu);
         }
 }
 
@@ -1002,7 +1007,7 @@ static void blk_register_tracepoints(void)
         WARN_ON(ret);
         ret = register_trace_block_plug(blk_add_trace_plug, NULL);
         WARN_ON(ret);
-        ret = register_trace_block_unplug_io(blk_add_trace_unplug_io, NULL);
+        ret = register_trace_block_unplug(blk_add_trace_unplug, NULL);
         WARN_ON(ret);
         ret = register_trace_block_split(blk_add_trace_split, NULL);
         WARN_ON(ret);
@@ -1017,7 +1022,7 @@ static void blk_unregister_tracepoints(void)
         unregister_trace_block_rq_remap(blk_add_trace_rq_remap, NULL);
         unregister_trace_block_bio_remap(blk_add_trace_bio_remap, NULL);
         unregister_trace_block_split(blk_add_trace_split, NULL);
-        unregister_trace_block_unplug_io(blk_add_trace_unplug_io, NULL);
+        unregister_trace_block_unplug(blk_add_trace_unplug, NULL);
         unregister_trace_block_plug(blk_add_trace_plug, NULL);
         unregister_trace_block_sleeprq(blk_add_trace_sleeprq, NULL);
         unregister_trace_block_getrq(blk_add_trace_getrq, NULL);
@@ -1332,6 +1337,7 @@ static const struct {
         [__BLK_TA_COMPLETE]     = {{  "C", "complete" },   blk_log_with_error },
         [__BLK_TA_PLUG]         = {{  "P", "plug" },       blk_log_plug },
         [__BLK_TA_UNPLUG_IO]    = {{  "U", "unplug_io" },  blk_log_unplug },
+        [__BLK_TA_UNPLUG_TIMER] = {{ "UT", "unplug_timer" }, blk_log_unplug },
         [__BLK_TA_INSERT]       = {{  "I", "insert" },     blk_log_generic },
         [__BLK_TA_SPLIT]        = {{  "X", "split" },      blk_log_split },
         [__BLK_TA_BOUNCE]       = {{  "B", "bounce" },     blk_log_generic },