From: Steven Rostedt (VMware) rostedt@goodmis.org
commit 7e0a9220467dbcfdc5bc62825724f3e52e50ab31 upstream.
On some archs, the idle task can call into cpu_suspend(). The cpu_suspend() will disable or pause function graph tracing, as there's some paths in bringing down the CPU that can have issues with its return address being modified. The task_struct structure has a "tracing_graph_pause" atomic counter, that when set to something other than zero, the function graph tracer will not modify the return address.
The problem is that the tracing_graph_pause counter is initialized when the function graph tracer is enabled. This can corrupt the counter for the idle task if it is suspended in these architectures.
CPU 1 CPU 2 ----- ----- do_idle() cpu_suspend() pause_graph_tracing() task_struct->tracing_graph_pause++ (0 -> 1)
start_graph_tracing() for_each_online_cpu(cpu) { ftrace_graph_init_idle_task(cpu) task-struct->tracing_graph_pause = 0 (1 -> 0)
unpause_graph_tracing() task_struct->tracing_graph_pause-- (0 -> -1)
The above should have gone from 1 to zero, and enabled function graph tracing again. But instead, it is set to -1, which keeps it disabled.
There's no reason that the field tracing_graph_pause on the task_struct can not be initialized at boot up.
Cc: stable@vger.kernel.org Fixes: 380c4b1411ccd ("tracing/function-graph-tracer: append the tracing_graph_flag") Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211339 Reported-by: pierre.gondois@arm.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/ftrace.h | 4 +++- kernel/trace/ftrace.c | 2 -- 2 files changed, 3 insertions(+), 3 deletions(-)
--- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -783,7 +783,9 @@ typedef int (*trace_func_graph_ent_t)(st #ifdef CONFIG_FUNCTION_GRAPH_TRACER
/* for init task */ -#define INIT_FTRACE_GRAPH .ret_stack = NULL, +#define INIT_FTRACE_GRAPH \ + .ret_stack = NULL, \ + .tracing_graph_pause = ATOMIC_INIT(0),
/* * Stack of return addresses for functions --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -5803,7 +5803,6 @@ static int alloc_retstack_tasklist(struc }
if (t->ret_stack == NULL) { - atomic_set(&t->tracing_graph_pause, 0); atomic_set(&t->trace_overrun, 0); t->curr_ret_stack = -1; /* Make sure the tasks see the -1 first: */ @@ -6015,7 +6014,6 @@ static DEFINE_PER_CPU(struct ftrace_ret_ static void graph_init_task(struct task_struct *t, struct ftrace_ret_stack *ret_stack) { - atomic_set(&t->tracing_graph_pause, 0); atomic_set(&t->trace_overrun, 0); t->ftrace_timestamp = 0; /* make curr_ret_stack visible before we add the ret_stack */