From: "Steven Rostedt (Red Hat)" <rost...@goodmis.org> When the first function probe is added and the function tracer is updated the functions are modified to call the probe. But when a second function is added, it updates the function records to have the second function also update, but it fails to update the actual function itself.
This prevents the second (or third or forth and so on) probes
from having their functions called.
# echo vfs_symlink:enable_event:sched:sched_switch > set_ftrace_filter
# echo vfs_unlink:enable_event:sched:sched_switch > set_ftrace_filter
# cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 0/0 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
# touch /tmp/a
# rm /tmp/a
# cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 0/0 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
# ln -s /tmp/a
# cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 414/414 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
<idle>-0 [000] d..3 2847.923031: sched_switch:
prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=bash
next_pid=2786 next_prio=120
<...>-3114 [001] d..4 2847.923035: sched_switch: prev_comm=ln
prev_pid=3114 prev_prio=120 prev_state=x ==> next_comm=swapper/1 next_pid=0
next_prio=120
bash-2786 [000] d..3 2847.923535: sched_switch: prev_comm=bash
prev_pid=2786 prev_prio=120 prev_state=S ==> next_comm=kworker/0:1 next_pid=34
next_prio=120
kworker/0:1-34 [000] d..3 2847.923552: sched_switch:
prev_comm=kworker/0:1 prev_pid=34 prev_prio=120 prev_state=S ==>
next_comm=swapper/0 next_pid=0 next_prio=120
<idle>-0 [002] d..3 2847.923554: sched_switch:
prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=sshd
next_pid=2783 next_prio=120
sshd-2783 [002] d..3 2847.923660: sched_switch: prev_comm=sshd
prev_pid=2783 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0
next_prio=120
Still need to update the functions even though the probe itself
does not need to be registered again when added a new probe.
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
---
kernel/trace/ftrace.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index dcca9fa..b549b0f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2941,8 +2941,12 @@ static void __enable_ftrace_function_probe(void)
int ret;
int i;
- if (ftrace_probe_registered)
+ if (ftrace_probe_registered) {
+ /* still need to update the function call sites */
+ if (ftrace_enabled)
+ ftrace_run_update_code(FTRACE_UPDATE_CALLS);
return;
+ }
for (i = 0; i < FTRACE_FUNC_HASHSIZE; i++) {
struct hlist_head *hhd = &ftrace_func_hash[i];
--
1.7.10.4
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