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From:   Waiman Long <longman@redhat.com>
To:     Jens Axboe <axboe@kernel.dk>, Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ming Lei <ming.lei@redhat.com>,
        Waiman Long <longman@redhat.com>
Subject: [PATCH] blk-iocost: Fix systemtap error on iocost_ioc_vrate_adj
Date:   Tue, 21 Apr 2020 09:07:55 -0400
Message-Id: <20200421130755.18370-1-longman@redhat.com>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 =E2=80=98;=E2=80=99, =E2=80=98,=E2=80=99 or =E2=80=98)=E2=
=80=99 before =E2=80=98*=E2=80=99 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")
Signed-off-by: Waiman Long <longman@redhat.com>
---
 block/blk-iocost.c            | 4 ++--
 include/trace/events/iocost.h | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index db35ee682294..3ab0c1c704b6 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1591,7 +1591,7 @@ static void ioc_timer_fn(struct timer_list *timer)
 				      vrate_min, vrate_max);
 		}
=20
-		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);
=20
@@ -1600,7 +1600,7 @@ static void ioc_timer_fn(struct timer_list *timer)
 			ioc->period_us * vrate * INUSE_MARGIN_PCT, 100);
 	} else if (ioc->busy_level !=3D 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);
 	}
=20
diff --git a/include/trace/events/iocost.h b/include/trace/events/iocost.=
h
index 7ecaa65b7106..c2f580fd371b 100644
--- a/include/trace/events/iocost.h
+++ b/include/trace/events/iocost.h
@@ -130,7 +130,7 @@ DEFINE_EVENT(iocg_inuse_update, iocost_inuse_reset,
=20
 TRACE_EVENT(iocost_ioc_vrate_adj,
=20
-	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),
=20
@@ -155,8 +155,8 @@ TRACE_EVENT(iocost_ioc_vrate_adj,
 		__entry->old_vrate =3D atomic64_read(&ioc->vtime_rate);;
 		__entry->new_vrate =3D new_vrate;
 		__entry->busy_level =3D ioc->busy_level;
-		__entry->read_missed_ppm =3D (*missed_ppm)[READ];
-		__entry->write_missed_ppm =3D (*missed_ppm)[WRITE];
+		__entry->read_missed_ppm =3D missed_ppm[READ];
+		__entry->write_missed_ppm =3D missed_ppm[WRITE];
 		__entry->rq_wait_pct =3D rq_wait_pct;
 		__entry->nr_lagging =3D nr_lagging;
 		__entry->nr_shortages =3D nr_shortages;
--=20
2.18.1