linux-kernel - [PATCH 5.6 057/106] blk-iocost: Fix error on iocost_ioc_vrate

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Date:   Fri,  1 May 2020 15:23:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Tejun Heo <tj@...nel.org>, Waiman Long <longman@...hat.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.6 057/106] blk-iocost: Fix error on iocost_ioc_vrate_adj

From: Waiman Long <longman@...hat.com>

commit d6c8e949a35d6906d6c03a50e9a9cdf4e494528a upstream.

Systemtap 4.2 is unable to correctly interpret the "u32 (*missed_ppm)[2]"
argument of the iocost_ioc_vrate_adj trace entry defined in
include/trace/events/iocost.h leading to the following error:

  /tmp/stapAcz0G0/stap_c89c58b83cea1724e26395efa9ed4939_6321_aux_6.c:78:8:
  error: expected ‘;’, ‘,’ or ‘)’ before ‘*’ token
   , u32[]* __tracepoint_arg_missed_ppm

That argument type is indeed rather complex and hard to read. Looking
at block/blk-iocost.c. It is just a 2-entry u32 array. By simplifying
the argument to a simple "u32 *missed_ppm" and adjusting the trace
entry accordingly, the compilation error was gone.

Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Acked-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Waiman Long <longman@...hat.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/blk-iocost.c            |    4 ++--
 include/trace/events/iocost.h |    6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1594,7 +1594,7 @@ skip_surplus_transfers:
 				      vrate_min, vrate_max);
 		}
 
-		trace_iocost_ioc_vrate_adj(ioc, vrate, &missed_ppm, rq_wait_pct,
+		trace_iocost_ioc_vrate_adj(ioc, vrate, missed_ppm, rq_wait_pct,
 					   nr_lagging, nr_shortages,
 					   nr_surpluses);
 
@@ -1603,7 +1603,7 @@ skip_surplus_transfers:
 			ioc->period_us * vrate * INUSE_MARGIN_PCT, 100);
 	} else if (ioc->busy_level != prev_busy_level || nr_lagging) {
 		trace_iocost_ioc_vrate_adj(ioc, atomic64_read(&ioc->vtime_rate),
-					   &missed_ppm, rq_wait_pct, nr_lagging,
+					   missed_ppm, rq_wait_pct, nr_lagging,
 					   nr_shortages, nr_surpluses);
 	}
 
--- a/include/trace/events/iocost.h
+++ b/include/trace/events/iocost.h
@@ -130,7 +130,7 @@ DEFINE_EVENT(iocg_inuse_update, iocost_i
 
 TRACE_EVENT(iocost_ioc_vrate_adj,
 
-	TP_PROTO(struct ioc *ioc, u64 new_vrate, u32 (*missed_ppm)[2],
+	TP_PROTO(struct ioc *ioc, u64 new_vrate, u32 *missed_ppm,
 		u32 rq_wait_pct, int nr_lagging, int nr_shortages,
 		int nr_surpluses),
 
@@ -155,8 +155,8 @@ TRACE_EVENT(iocost_ioc_vrate_adj,
 		__entry->old_vrate = atomic64_read(&ioc->vtime_rate);;
 		__entry->new_vrate = new_vrate;
 		__entry->busy_level = ioc->busy_level;
-		__entry->read_missed_ppm = (*missed_ppm)[READ];
-		__entry->write_missed_ppm = (*missed_ppm)[WRITE];
+		__entry->read_missed_ppm = missed_ppm[READ];
+		__entry->write_missed_ppm = missed_ppm[WRITE];
 		__entry->rq_wait_pct = rq_wait_pct;
 		__entry->nr_lagging = nr_lagging;
 		__entry->nr_shortages = nr_shortages;