Commit 8306f5c7 authored by Vasily Averin's avatar Vasily Averin Committed by Greg Kroah-Hartman

ftrace: fpid_next() should increase position index

[ Upstream commit e4075e8b ]

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/[email protected]

https://bugzilla.kernel.org/show_bug.cgi?id=206283Signed-off-by: default avatarVasily Averin <[email protected]>
Signed-off-by: default avatarSteven Rostedt (VMware) <[email protected]>
Signed-off-by: default avatarSasha Levin <[email protected]>
parent b694a3ef
......@@ -7038,9 +7038,10 @@ 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);
}
......
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