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Date: Mon, 14 Apr 2014 13:09:44 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To: Takao Indoh <indou.takao@...fujitsu.com>
Cc: rusty@...tcorp.com.au, rostedt@...dmis.org,
linux-kernel@...r.kernel.org,
ltc-kernel@...yrl.intra.hitachi.co.jp,
"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>,
Satoshi Oshima <satoshi.oshima.fk@...achi.com>
Subject: Re: Re: [PATCH] module: Introduce MODULE_STATE_COMING_FINAL to
avoid ftrace warning
(2014/04/14 11:49), Takao Indoh wrote:
> 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>
As Steven said, it should have his signed-off too, anyway,
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Thank you,
>> ---
>> 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,
>>
>
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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