From af7ebb5fa0769c387e5542799bd503325803c068 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 14 Mar 2025 12:03:09 +0900 Subject: [PATCH] fgraph: Still initialize idle shadow stacks when starting BugLink: https://bugs.launchpad.net/bugs/2102266 commit cc252bb592638e0f7aea40d580186c36d89526b8 upstream. A bug was discovered where the idle shadow stacks were not initialized for offline CPUs when starting function graph tracer, and when they came online they were not traced due to the missing shadow stack. To fix this, the idle task shadow stack initialization was moved to using the CPU hotplug callbacks. But it removed the initialization when the function graph was enabled. The problem here is that the hotplug callbacks are called when the CPUs come online, but the idle shadow stack initialization only happens if function graph is currently active. This caused the online CPUs to not get their shadow stack initialized. The idle shadow stack initialization still needs to be done when the function graph is registered, as they will not be allocated if function graph is not registered. Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Link: https://lore.kernel.org/20241211135335.094ba282@batman.local.home Fixes: 2c02f7375e65 ("fgraph: Use CPU hotplug mechanism to initialize idle shadow stacks") Reported-by: Linus Walleij Tested-by: Linus Walleij Closes: https://lore.kernel.org/all/CACRpkdaTBrHwRbbrphVy-=SeDz6MSsXhTKypOtLrTQ+DgGAOcQ@mail.gmail.com/ Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman [koichiroden: adjusted context due to missing commit: 42675b723b48 ("function_graph: Convert ret_stack to a series of longs")] Signed-off-by: Koichiro Den Signed-off-by: Mehmet Basaran --- kernel/trace/fgraph.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c index b2701a5338ad..beb3c3a45df5 100644 --- a/kernel/trace/fgraph.c +++ b/kernel/trace/fgraph.c @@ -600,7 +600,7 @@ void ftrace_graph_exit_task(struct task_struct *t) static int start_graph_tracing(void) { struct ftrace_ret_stack **ret_stack_list; - int ret; + int ret, cpu; ret_stack_list = kmalloc_array(FTRACE_RETSTACK_ALLOC_SIZE, sizeof(struct ftrace_ret_stack *), @@ -609,6 +609,12 @@ static int start_graph_tracing(void) if (!ret_stack_list) return -ENOMEM; + /* The cpu_boot init_task->ret_stack will never be freed */ + for_each_online_cpu(cpu) { + if (!idle_task(cpu)->ret_stack) + ftrace_graph_init_idle_task(idle_task(cpu), cpu); + } + do { ret = alloc_retstack_tasklist(ret_stack_list); } while (ret == -EAGAIN);