Commit bf08949c authored Dec 03, 2019 by Masami Hiramatsu Committed by Jessica Yu Dec 09, 2019

modules: lockdep: Suppress suspicious RCU usage warning



While running kprobe module test, find_module_all() caused
a suspicious RCU usage warning.

-----
 =============================
 WARNING: suspicious RCU usage
 5.4.0-next-20191202+ #63 Not tainted
 -----------------------------
 kernel/module.c:619 RCU-list traversed in non-reader section!!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 1 lock held by rmmod/642:
  #0: ffffffff8227da80 (module_mutex){+.+.}, at: __x64_sys_delete_module+0x9a/0x230

 stack backtrace:
 CPU: 0 PID: 642 Comm: rmmod Not tainted 5.4.0-next-20191202+ #63
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
 Call Trace:
  dump_stack+0x71/0xa0
  find_module_all+0xc1/0xd0
  __x64_sys_delete_module+0xac/0x230
  ? do_syscall_64+0x12/0x1f0
  do_syscall_64+0x50/0x1f0
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
 RIP: 0033:0x4b6d49
-----

This is because list_for_each_entry_rcu(modules) is called
without rcu_read_lock(). This is safe because the module_mutex
is locked.

Pass lockdep_is_held(&module_mutex) to the list_for_each_entry_rcu()
to suppress this warning, This also fixes similar issue in
mod_find() and each_symbol_section().

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Jessica Yu <jeyu@kernel.org>

parent e42617b8

kernel/module.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -214,7 +214,8 @@ static struct module *mod_find(unsigned long addr)
		{
		struct module *mod;

		list_for_each_entry_rcu(mod, &modules, list) {
		list_for_each_entry_rcu(mod, &modules, list,
		lockdep_is_held(&module_mutex)) {
		if (within_module(addr, mod))
		return mod;
		}
		@@ -448,7 +449,8 @@ bool each_symbol_section(bool (fn)(const struct symsearch arr,
		if (each_symbol_in_section(arr, ARRAY_SIZE(arr), NULL, fn, data))
		return true;

		list_for_each_entry_rcu(mod, &modules, list) {
		list_for_each_entry_rcu(mod, &modules, list,
		lockdep_is_held(&module_mutex)) {
		struct symsearch arr[] = {
		{ mod->syms, mod->syms + mod->num_syms, mod->crcs,
		NOT_GPL_ONLY, false },
		@@ -616,7 +618,8 @@ static struct module find_module_all(const char name, size_t len,

		module_assert_mutex_or_preempt();

		list_for_each_entry_rcu(mod, &modules, list) {
		list_for_each_entry_rcu(mod, &modules, list,
		lockdep_is_held(&module_mutex)) {
		if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
		continue;
		if (strlen(mod->name) == len && !memcmp(mod->name, name, len))

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