From: Steven Rostedt <rostedt@xxxxxxxxxxx> 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 '<idle>' per_cpu/cpu1/trace | head Before, nothing would show up. After: 1) <idle>-0 | 0.811 us | __enqueue_entity(); 1) <idle>-0 | 5.626 us | } /* enqueue_entity */ 1) <idle>-0 | | dl_server_update_idle_time() { 1) <idle>-0 | | dl_scaled_delta_exec() { 1) <idle>-0 | 0.450 us | arch_scale_cpu_capacity(); 1) <idle>-0 | 1.242 us | } 1) <idle>-0 | 1.908 us | } 1) <idle>-0 | | dl_server_start() { 1) <idle>-0 | | enqueue_dl_entity() { 1) <idle>-0 | | task_contending() { Note, if tracing stops and restarts, the old way would then initialize the onlined CPUs. Cc: stable@xxxxxxxxxxxxxxx Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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) <rostedt@xxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/trace/fgraph.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-) --- a/kernel/trace/fgraph.c +++ b/kernel/trace/fgraph.c @@ -1160,19 +1160,13 @@ void fgraph_update_pid_func(void) static int start_graph_tracing(void) { unsigned long **ret_stack_list; - int ret, cpu; + int ret; ret_stack_list = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL); 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); @@ -1242,14 +1236,34 @@ static void ftrace_graph_disable_direct( fgraph_direct_gops = &fgraph_stub; } +/* 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 command = 0; int ret = 0; int i = -1; 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; + } + if (!fgraph_array[0]) { /* The array must always have real data on it */ for (i = 0; i < FGRAPH_ARRAY_SIZE; i++) Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are queue-6.11/fgraph-use-cpu-hotplug-mechanism-to-initialize-idle-shadow-stacks.patch queue-6.11/mm-khugepaged-fix-the-arguments-order-in-khugepaged_collapse_file-trace-point.patch