[PATCH] module: Introduce MODULE_STATE_COMING_FINAL to avoid ftrace warning
From: Takao Indoh
Date: Wed Apr 02 2014 - 03:55:05 EST
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@xxxxxxxxxxxxxx>
---
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,
--
1.8.3.1
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