ftrace: Update func_pos in t_start() when all functions are enabled
If all functions are enabled, there's a comment displayed in the file to
denote that:
# cd /sys/kernel/debug/tracing
# cat set_ftrace_filter
#### all functions enabled ####
If a function trigger is set, those are displayed as well:
# echo schedule:traceoff >> /debug/tracing/set_ftrace_filter
# cat set_ftrace_filter
#### all functions enabled ####
schedule:traceoff:unlimited
But if you read that file with dd, the output can change:
# dd if=/debug/tracing/set_ftrace_filter bs=1
#### all functions enabled ####
32+0 records in
32+0 records out
32 bytes copied, 7.0237e-05 s, 456 kB/s
This is because the "pos" variable is updated for the comment, but func_pos
is not. "func_pos" is used by the triggers (or hashes) to know how many
functions were printed and it bases its index from the pos - func_pos.
func_pos should be 1 to count for the comment printed. But since it is not,
t_hash_start() thinks that one trigger was already printed.
The cat gets to t_hash_start() via t_next() and not t_start() which updates
both pos and func_pos.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4215308..d4b18ce 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3230,6 +3230,7 @@
*/
if ((iter->flags & (FTRACE_ITER_FILTER | FTRACE_ITER_NOTRACE)) &&
ftrace_hash_empty(iter->hash)) {
+ iter->func_pos = 1; /* Account for the message */
if (*pos > 0)
return t_hash_start(m, pos);
iter->flags |= FTRACE_ITER_PRINTALL;