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.ta...@jp.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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