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    Subject[PATCH AUTOSEL 5.5 171/542] modules: lockdep: Suppress suspicious RCU usage warning
    Date
    From: Masami Hiramatsu <mhiramat@kernel.org>

    [ Upstream commit bf08949cc8b98b7d1e20cfbba169a5938d42dae8 ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/module.c | 9 ++++++---
    1 file changed, 6 insertions(+), 3 deletions(-)

    diff --git a/kernel/module.c b/kernel/module.c
    index 8785e31c2dd0f..d83edc3a41a33 100644
    --- a/kernel/module.c
    +++ b/kernel/module.c
    @@ -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))
    --
    2.20.1
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