[Devel] [PATCH vz7 v2 2/2] block: store exec_ub on struct request and use it

[Konstantin Khorenko]

Good calltrace: we set proper exec_ub in ploop_req_state_process()
and later process requests - accounting goes to correct ub.

loop35172  6275 [002]   755.716683:  probe:ub_writeback_io_3:
			(ffffffff813547aa) ub=0xffff880394a04000
                  5547ab deadline_add_request
                  52e76a __elv_add_request
                  536350 blk_flush_plug_list
                  5365aa blk_queue_bio
                  5345bb generic_make_request
                  534843 submit_bio
                    43e4 dio_submit ([pio_direct])
                    616f ploop_entry_request ([ploop])
                    7209 ploop_req_state_process ([ploop])
                    7735 ploop_thread ([ploop])

Bad calltrace: due to task->plug io batching we may miss calling
ploop_req_state_process() and process requests with ploop thread's ub == ub0:

ploop35172  6275 [002]   755.716763:  probe:ub_writeback_io_2:
			 (ffffffff81354785) ub=0xffffffff81f7b880 (ub0!!!)
                  554786 deadline_add_request
                  52e76a __elv_add_request
                  536350 blk_flush_plug_list
                  536714 blk_finish_plug
                    1a93 ploop_wait ([ploop])
                    77a1 ploop_thread ([ploop])

=> need to store exec_ub in struct request as well.

We are safe to check for NULL request:req_ub to detect set it or not
because request is zeroed on creation:

   get_request
    __get_request
     blk_rq_init
      memset(rq, 0, sizeof(*rq));

https://jira.sw.ru/browse/PSBM-86910

Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>

v2 changes:
 - store exec_ub to request in __get_request() instead of
   blk_queue_bio(), this covers more potential cases
 - __elv_add_request() must get/put ub because request can be freed
   before the end of __elv_add_request() execution
---
 block/blk-cgroup.h     | 15 +++++++++++++++
 block/blk-core.c       |  7 +++++++
 block/elevator.c       | 17 +++++++++++++++++
 include/linux/blkdev.h |  1 +
 4 files changed, 40 insertions(+)

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 320a357c7525..6c6ad5c336cd 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -389,6 +389,20 @@ static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl)
 	rq->rl = rl;
 }
 
+/**
+ * blk_rq_set_ub - associate a request with a user beancounter
+ * @rq: request of interest
+ *
+ * Store current exec_ub in @rq so later we can use it while adding the request
+ * to elevator.
+ */
+static inline void blk_rq_set_ub(struct request *rq)
+{
+#ifdef CONFIG_BEANCOUNTERS
+	rq->req_ub = get_beancounter(get_exec_ub());
+#endif
+}
+
 /**
  * blk_rq_rl - return the request_list a request came from
  * @rq: request of interest
@@ -595,6 +609,7 @@ static inline struct request_list *blk_get_rl(struct request_queue *q,
 					      struct bio *bio) { return &q->root_rl; }
 static inline void blk_put_rl(struct request_list *rl) { }
 static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl) { }
+static inline void blk_rq_set_ub(struct request *rq) { }
 static inline struct request_list *blk_rq_rl(struct request *rq) { return &rq->q->root_rl; }
 
 #define blk_queue_for_each_rl(rl, q)	\
diff --git a/block/blk-core.c b/block/blk-core.c
index 45e2d9a93fc8..893a50b0214a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -950,6 +950,12 @@ EXPORT_SYMBOL(blk_get_queue);
 
 static inline void blk_free_request(struct request_list *rl, struct request *rq)
 {
+#ifdef CONFIG_BEANCOUNTERS
+	if (rq->req_ub) {
+		put_beancounter(rq->req_ub);
+		rq->req_ub = NULL;
+	}
+#endif
 	if (rq->cmd_flags & REQ_ELVPRIV) {
 		elv_put_request(rl->q, rq);
 		if (rq->elv.icq)
@@ -1197,6 +1203,7 @@ static struct request *__get_request(struct request_list *rl, int rw_flags,
 
 	blk_rq_init(q, rq);
 	blk_rq_set_rl(rq, rl);
+	blk_rq_set_ub(rq);
 	rq->cmd_flags = rw_flags | REQ_ALLOCED;
 	if (flags & BLK_MQ_REQ_PREEMPT)
 		rq->cmd_flags |= REQ_PREEMPT;
diff --git a/block/elevator.c b/block/elevator.c
index e81087c3e72d..13097074c157 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -658,6 +658,17 @@ void elv_drain_elevator(struct request_queue *q)
 
 void __elv_add_request(struct request_queue *q, struct request *rq, int where)
 {
+#ifdef CONFIG_BEANCOUNTERS
+	struct user_beancounter *ub = NULL;
+	if (rq->req_ub) {
+		/*
+		 * Request can be already freed at the end of func,
+		 * so get beancounter.
+		 */
+		get_beancounter(rq->req_ub);
+		ub = set_exec_ub(rq->req_ub);
+	}
+#endif
 	trace_block_rq_insert(q, rq);
 
 	blk_pm_add_request(q, rq);
@@ -734,6 +745,12 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where)
 		       __func__, where);
 		BUG();
 	}
+#ifdef CONFIG_BEANCOUNTERS
+	if (ub) {
+		ub = set_exec_ub(ub);
+		put_beancounter(ub);
+	}
+#endif
 }
 EXPORT_SYMBOL(__elv_add_request);
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 55cba7563e57..49bb13fa4d4f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -200,6 +200,7 @@ struct request {
 #endif
 
 	unsigned short ioprio;
+	struct user_beancounter *req_ub;
 
 	void *special;		/* opaque pointer available for LLD use */
 	char *buffer;		/* kaddr of the current segment if available */
-- 
2.15.1