[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20200227132246.178585643@linuxfoundation.org>
Date: Thu, 27 Feb 2020 14:36:17 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Vasily Averin <vvs@...tuozzo.com>,
"Steven Rostedt (VMware)" <rostedt@...dmis.org>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 103/165] ftrace: fpid_next() should increase position index
From: Vasily Averin <vvs@...tuozzo.com>
[ Upstream commit e4075e8bdffd93a9b6d6e1d52fabedceeca5a91b ]
if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.
Without patch:
# dd bs=4 skip=1 if=/sys/kernel/tracing/set_ftrace_pid
dd: /sys/kernel/tracing/set_ftrace_pid: cannot skip to specified offset
id
no pid
2+1 records in
2+1 records out
10 bytes copied, 0.000213285 s, 46.9 kB/s
Notice the "id" followed by "no pid".
With the patch:
# dd bs=4 skip=1 if=/sys/kernel/tracing/set_ftrace_pid
dd: /sys/kernel/tracing/set_ftrace_pid: cannot skip to specified offset
id
0+1 records in
0+1 records out
3 bytes copied, 0.000202112 s, 14.8 kB/s
Notice that it only prints "id" and not the "no pid" afterward.
Link: http://lkml.kernel.org/r/4f87c6ad-f114-30bb-8506-c32274ce2992@virtuozzo.com
https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
kernel/trace/ftrace.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 71a40e5c3a9f0..2ae98f8bce81b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5455,9 +5455,10 @@ static void *fpid_next(struct seq_file *m, void *v, loff_t *pos)
struct trace_array *tr = m->private;
struct trace_pid_list *pid_list = rcu_dereference_sched(tr->function_pids);
- if (v == FTRACE_NO_PIDS)
+ if (v == FTRACE_NO_PIDS) {
+ (*pos)++;
return NULL;
-
+ }
return trace_pid_next(pid_list, v, pos);
}
--
2.20.1
Powered by blists - more mailing lists