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authorVasily Averin <vvs@virtuozzo.com>2020-01-24 10:02:56 +0300
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2020-01-30 09:46:27 -0500
commite4075e8bdffd93a9b6d6e1d52fabedceeca5a91b (patch)
treebf28d90ef0aee9ff10f9396018bfc2946af8de30 /kernel/trace
parent64ae572bc7d0060429e40e1c8d803ce5eb31a0d6 (diff)
downloadlinux-e4075e8bdffd93a9b6d6e1d52fabedceeca5a91b.tar.bz2
ftrace: fpid_next() should increase position index
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@virtuozzo.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/ftrace.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index fdb1a9532420..0e9612c30995 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7026,9 +7026,10 @@ 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);
}