Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Zheng Yejian <zhengyejian1@huawei.com>
To:     <rostedt@goodmis.org>, <mhiramat@kernel.org>, <zanussi@kernel.org>
CC:     <linux-kernel@vger.kernel.org>,
        <linux-trace-kernel@vger.kernel.org>, <zhengyejian1@huawei.com>
Subject: [PATCH] tracing: Fix issue of missing one synthetic field
Date:   Wed, 7 Dec 2022 17:15:57 +0800
Message-ID: <20221207091557.3137904-1-zhengyejian1@huawei.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7BIT
Content-Type:   text/plain; charset=US-ASCII
Precedence: bulk

The maximum number of synthetic fields supported is defined as
SYNTH_FIELDS_MAX which value currently is 64, but it actually fails
when try to generate a synthetic event with 64 fields by executing like:

  # echo "my_synth_event int v1; int v2; int v3; int v4; int v5; int v6;\
   int v7; int v8; int v9; int v10; int v11; int v12; int v13; int v14;\
   int v15; int v16; int v17; int v18; int v19; int v20; int v21; int v22;\
   int v23; int v24; int v25; int v26; int v27; int v28; int v29; int v30;\
   int v31; int v32; int v33; int v34; int v35; int v36; int v37; int v38;\
   int v39; int v40; int v41; int v42; int v43; int v44; int v45; int v46;\
   int v47; int v48; int v49; int v50; int v51; int v52; int v53; int v54;\
   int v55; int v56; int v57; int v58; int v59; int v60; int v61; int v62;\
   int v63; int v64" >> /sys/kernel/tracing/synthetic_events

Correct the field counting to fix it.

Fixes: c9e759b1e845 ("tracing: Rework synthetic event command parsing")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
 kernel/trace/trace_events_synth.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index c3b582d19b62..67592eed0be8 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -1282,12 +1282,12 @@ static int __create_synth_event(const char *name, const char *raw_fields)
 				goto err_free_arg;
 			}
 
-			fields[n_fields++] = field;
 			if (n_fields == SYNTH_FIELDS_MAX) {
 				synth_err(SYNTH_ERR_TOO_MANY_FIELDS, 0);
 				ret = -EINVAL;
 				goto err_free_arg;
 			}
+			fields[n_fields++] = field;
 
 			n_fields_this_loop++;
 		}
-- 
2.25.1