From 949a2659fb8896992311db22d37a350758a498e3 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 18 Oct 2024 21:43:00 -0400 Subject: [PATCH] fgraph: Use CPU hotplug mechanism to initialize idle shadow stacks BugLink: https://bugs.launchpad.net/bugs/2097393 commit 2c02f7375e658ae93d57a31a66f91b62754ef8f1 upstream. The function graph infrastructure allocates a shadow stack for every task when enabled. This includes the idle tasks. The first time the function graph is invoked, the shadow stacks are created and never freed until the task exits. This includes the idle tasks. Only the idle tasks that were for online CPUs had their shadow stacks created when function graph tracing started. If function graph tracing is enabled and a CPU comes online, the idle task representing that CPU will not have its shadow stack created, and all function graph tracing for that idle task will be silently dropped. Instead, use the CPU hotplug mechanism to allocate the idle shadow stacks. This will include idle tasks for CPUs that come online during tracing. This issue can be reproduced by: # cd /sys/kernel/tracing # echo 0 > /sys/devices/system/cpu/cpu1/online # echo 0 > set_ftrace_pid # echo function_graph > current_tracer # echo 1 > options/funcgraph-proc # echo 1 > /sys/devices/system/cpu/cpu1 # grep '' per_cpu/cpu1/trace | head Before, nothing would show up. After: 1) -0 | 0.811 us | __enqueue_entity(); 1) -0 | 5.626 us | } /* enqueue_entity */ 1) -0 | | dl_server_update_idle_time() { 1) -0 | | dl_scaled_delta_exec() { 1) -0 | 0.450 us | arch_scale_cpu_capacity(); 1) -0 | 1.242 us | } 1) -0 | 1.908 us | } 1) -0 | | dl_server_start() { 1) -0 | | enqueue_dl_entity() { 1) -0 | | task_contending() { Note, if tracing stops and restarts, the old way would then initialize the onlined CPUs. Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Mark Rutland Cc: Thomas Gleixner Link: https://lore.kernel.org/20241018214300.6df82178@rorschach Fixes: 868baf07b1a25 ("ftrace: Fix memory leak with function graph and cpu hotplug") Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman Signed-off-by: Manuel Diewald Signed-off-by: Koichiro Den --- kernel/trace/fgraph.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-) diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c index c83c005e654e..cdcaf7ddd68d 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, cpu; + int ret; ret_stack_list = kmalloc_array(FTRACE_RETSTACK_ALLOC_SIZE, sizeof(struct ftrace_ret_stack *), @@ -609,12 +609,6 @@ 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); @@ -630,12 +624,32 @@ static int start_graph_tracing(void) return ret; } +/* The cpu_boot init_task->ret_stack will never be freed */ +static int fgraph_cpu_init(unsigned int cpu) +{ + if (!idle_task(cpu)->ret_stack) + ftrace_graph_init_idle_task(idle_task(cpu), cpu); + return 0; +} + int register_ftrace_graph(struct fgraph_ops *gops) { + static bool fgraph_initialized; int ret = 0; mutex_lock(&ftrace_lock); + if (!fgraph_initialized) { + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "fgraph_idle_init", + fgraph_cpu_init, NULL); + if (ret < 0) { + pr_warn("fgraph: Error to init cpu hotplug support\n"); + return ret; + } + fgraph_initialized = true; + ret = 0; + } + /* we currently allow only one tracer registered at a time */ if (ftrace_graph_active) { ret = -EBUSY;