linux-kernel - [for-next][PATCH 05/21] tracing: eval_map_next() should always increase position index

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Date:   Thu, 30 Jan 2020 09:47:48 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vasily Averin <vvs@...tuozzo.com>
Subject: [for-next][PATCH 05/21] tracing: eval_map_next() should always increase position index

From: Vasily Averin <vvs@...tuozzo.com>

if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

Link: http://lkml.kernel.org/r/7ad85b22-1866-977c-db17-88ac438bc764@virtuozzo.com

Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
[ This is not a bug fix, it just makes it "technically correct"
  which is why I applied it. NULL is only returned on an anomaly
  which triggers a WARN_ON ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6a28b1b9bf42..8d144fd94aa8 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5399,14 +5399,12 @@ static void *eval_map_next(struct seq_file *m, void *v, loff_t *pos)
 	 * Paranoid! If ptr points to end, we don't want to increment past it.
 	 * This really should never happen.
 	 */
+	(*pos)++;
 	ptr = update_eval_map(ptr);
 	if (WARN_ON_ONCE(!ptr))
 		return NULL;
 
 	ptr++;
-
-	(*pos)++;
-
 	ptr = update_eval_map(ptr);
 
 	return ptr;
-- 
2.24.1