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Date: Mon, 14 Apr 2014 11:49:25 +0900
From: Takao Indoh <indou.takao@...fujitsu.com>
To: rusty@...tcorp.com.au
CC: rostedt@...dmis.org, masami.hiramatsu.pt@...achi.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] module: Introduce MODULE_STATE_COMING_FINAL to avoid
ftrace warning
ping, any comments?
(2014/04/02 16:54), Takao Indoh wrote:
> This patch adds new module state MODULE_STATE_COMING_FINAL to avoid
> ftrace waring message when loading two modules simultaneously.
>
> The original patch was written by Steven Rostedt, see below.
> https://lkml.org/lkml/2014/3/24/242
>
> Ftrace waring message below is got when insmod two modules almost at the
> same time and at least one of them uses register_kprobe() in its
> module_init.
>
> [ 409.337936] ------------[ cut here ]------------
> [ 409.337945] WARNING: CPU: 12 PID: 10028 at /mnt/repos/linux/kernel/trace/ftrace.c:1716 ftrace_bug+0x206/0x270()
> (snip)
> [ 409.337983] Call Trace:
> [ 409.337990] [<ffffffff81547bfe>] dump_stack+0x45/0x56
> [ 409.337993] [<ffffffff81049a0d>] warn_slowpath_common+0x7d/0xa0
> [ 409.337997] [<ffffffffa0364000>] ? 0xffffffffa0363fff
> [ 409.337999] [<ffffffff81049aea>] warn_slowpath_null+0x1a/0x20
> [ 409.338001] [<ffffffff810e79f6>] ftrace_bug+0x206/0x270
> [ 409.338004] [<ffffffffa0364000>] ? 0xffffffffa0363fff
> [ 409.338006] [<ffffffff810e7d8e>] ftrace_process_locs+0x32e/0x710
> [ 409.338008] [<ffffffff810e8206>] ftrace_module_notify_enter+0x96/0xf0
> [ 409.338012] [<ffffffff81551dec>] notifier_call_chain+0x4c/0x70
> [ 409.338018] [<ffffffff8106fbfd>] __blocking_notifier_call_chain+0x4d/0x70
> [ 409.338020] [<ffffffff8106fc36>] blocking_notifier_call_chain+0x16/0x20
> [ 409.338026] [<ffffffff810bf3f4>] load_module+0x1f54/0x25d0
> [ 409.338028] [<ffffffff810baab0>] ? store_uevent+0x40/0x40
> [ 409.338031] [<ffffffff810bfbe6>] SyS_finit_module+0x86/0xb0
> [ 409.338036] [<ffffffff81556752>] system_call_fastpath+0x16/0x1b
> [ 409.338037] ---[ end trace e7e27c36e7a65831 ]---
> [ 409.338040] ftrace faulted on writing [<ffffffffa0364000>] handler_pre+0x0/0x10 [test2]
>
> This is the sequence when this problem occurs.
>
> <insmod module A>
> init_module
> load_module
> do_init_module
> do_one_initcall
> (module_init)
> register_kprobe
> arm_kprobe
> arm_kprobe_ftrace
> register_ftrace_function
> mutex_lock(&ftrace_lock) ------------------- (1)
> ftrace_startup
> ftrace_startup_enable
> ftrace_run_update_code
> ftrace_arch_code_modify_post_process
> set_all_modules_text_ro ------------ (2)
> mutex_unlock(&ftrace_lock) ----------------- (3)
>
> <insmod module B>
> init_module
> load_module
> do_init_module
> blocking_notifier_call_chain
> ftrace_module_notify_enter
> ftrace_init_module
> ftrace_process_locs
> mutex_lock(&ftrace_lock) ------------------------ (4)
> ftrace_update_code
> __ftrace_replace_code
> ftrace_make_nop
> ftrace_modify_code_direct
> do_ftrace_mod_code
> probe_kernel_write -------------------- (5)
>
> o Module A gets ftrace_lock at (1)
> o Module B also tries to get ftrace_lock at (4) somewhat late, and waits
> here because module A got it.
> o Module A sets all modules text to ReadOnly at (2), and then release
> ftrace_lock at (3)
> o Module B wakes up and tries to rewrite its text at (5), but it fails
> because it is already changed to RO at (2) by modules A. The ftrace
> waring message is outputted.
>
> This patch introduces MODULE_STATE_COMING_FINAL which means that the
> module is ready to be changed to ReadOnly. By this, the modules B is not
> change to RO at (2) because its state is still MODULE_STATE_COMING, so
> this warning message is avoided. Module B is changed to RO in the
> do_init_module() after comes back from notifier.
>
> Signed-off-by: Takao Indoh <indou.takao@...fujitsu.com>
> ---
> include/linux/module.h | 9 +++++----
> kernel/module.c | 13 ++++++++++++-
> 2 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index eaf60ff..32f4481 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -207,10 +207,11 @@ struct module_use {
> };
>
> enum module_state {
> - MODULE_STATE_LIVE, /* Normal state. */
> - MODULE_STATE_COMING, /* Full formed, running module_init. */
> - MODULE_STATE_GOING, /* Going away. */
> - MODULE_STATE_UNFORMED, /* Still setting it up. */
> + MODULE_STATE_LIVE, /* Normal state. */
> + MODULE_STATE_COMING, /* Full formed, running module_init. */
> + MODULE_STATE_COMING_FINAL, /* Ready to be changed to read only. */
> + MODULE_STATE_GOING, /* Going away. */
> + MODULE_STATE_UNFORMED, /* Still setting it up. */
> };
>
> /**
> diff --git a/kernel/module.c b/kernel/module.c
> index 8dc7f5e..94b9f91 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1033,6 +1033,9 @@ static ssize_t show_initstate(struct module_attribute *mattr,
> case MODULE_STATE_COMING:
> state = "coming";
> break;
> + case MODULE_STATE_COMING_FINAL:
> + state = "coming_final";
> + break;
> case MODULE_STATE_GOING:
> state = "going";
> break;
> @@ -1805,7 +1808,8 @@ void set_all_modules_text_ro(void)
>
> mutex_lock(&module_mutex);
> list_for_each_entry_rcu(mod, &modules, list) {
> - if (mod->state == MODULE_STATE_UNFORMED)
> + if (mod->state == MODULE_STATE_UNFORMED ||
> + mod->state == MODULE_STATE_COMING)
> continue;
> if ((mod->module_core) && (mod->core_text_size)) {
> set_page_attributes(mod->module_core,
> @@ -3024,6 +3028,13 @@ static int do_init_module(struct module *mod)
> blocking_notifier_call_chain(&module_notify_list,
> MODULE_STATE_COMING, mod);
>
> + /*
> + * This module must not be changed by set_all_modules_text_ro()
> + * until we get here. Otherwise notifiers that change text
> + * (like ftrace does) will break.
> + */
> + mod->state = MODULE_STATE_COMING_FINAL;
> +
> /* Set RO and NX regions for core */
> set_section_ro_nx(mod->module_core,
> mod->core_text_size,
>
--
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