Skip to content

Commit

Permalink
ftrace: Fix ftrace enable ordering of sysctl ftrace_enabled
Browse files Browse the repository at this point in the history
Some archs (specifically PowerPC), are sensitive with the ordering of
the enabling of the calls to function tracing and setting of the
function to use to be traced.

That is, update_ftrace_function() sets what function the ftrace_caller
trampoline should call. Some archs require this to be set before
calling ftrace_run_update_code().

Another bug was discovered, that ftrace_startup_sysctl() called
ftrace_run_update_code() directly. If the function the ftrace_caller
trampoline changes, then it will not be updated. Instead a call
to ftrace_startup_enable() should be called because it tests to see
if the callback changed since the code was disabled, and will
tell the arch to update appropriately. Most archs do not need this
notification, but PowerPC does.

The problem could be seen by the following commands:

 # echo 0 > /proc/sys/kernel/ftrace_enabled
 # echo function > /sys/kernel/debug/tracing/current_tracer
 # echo 1 > /proc/sys/kernel/ftrace_enabled
 # cat /sys/kernel/debug/tracing/trace

The trace will show that function tracing was not active.

Cc: stable@vger.kernel.org # 2.6.27+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
  • Loading branch information
Steven Rostedt (Red Hat) committed Mar 9, 2015
1 parent 1619dc3 commit 524a386
Showing 1 changed file with 3 additions and 3 deletions.
6 changes: 3 additions & 3 deletions kernel/trace/ftrace.c
Original file line number Diff line number Diff line change
Expand Up @@ -2710,7 +2710,7 @@ static void ftrace_startup_sysctl(void)
command = FTRACE_UPDATE_CALLS;
if (ftrace_graph_active)
command |= FTRACE_START_FUNC_RET;
ftrace_run_update_code(command);
ftrace_startup_enable(command);
}
}

Expand Down Expand Up @@ -5580,12 +5580,12 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,

if (ftrace_enabled) {

ftrace_startup_sysctl();

/* we are starting ftrace again */
if (ftrace_ops_list != &ftrace_list_end)
update_ftrace_function();

ftrace_startup_sysctl();

} else {
/* stopping ftrace calls (just send to ftrace_stub) */
ftrace_trace_function = ftrace_stub;
Expand Down

0 comments on commit 524a386

Please sign in to comment.