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From:   Song Liu <song@kernel.org>
Date:   Fri, 23 Sep 2022 17:54:23 -0700
Message-ID: <CAPhsuW42bjAEZwELabNKHpS2iWs9ps8NygU_G6cJ404PbJLi9Q@mail.gmail.com>
Subject: Re: [PATCH] ftrace: fix recursive locking direct_mutex in ftrace_modify_direct_caller
To:     open list <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     Kernel Team <kernel-team@fb.com>,
        "Naveen N . Rao" <naveen.n.rao@linux.vnet.ibm.com>
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Hi Steven,

Does this fix make sense to you?

Thanks,
Song

On Mon, Sep 19, 2022 at 10:30 AM Song Liu <song@kernel.org> wrote:
>
> Naveen reported recursive locking of direct_mutex with sample
> ftrace-direct-modify.ko:
>
> [   74.762406] WARNING: possible recursive locking detected
> [   74.762887] 6.0.0-rc6+ #33 Not tainted
> [   74.763216] --------------------------------------------
> [   74.763672] event-sample-fn/1084 is trying to acquire lock:
> [   74.764152] ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \
>     register_ftrace_function+0x1f/0x180
> [   74.764922]
> [   74.764922] but task is already holding lock:
> [   74.765421] ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \
>     modify_ftrace_direct+0x34/0x1f0
> [   74.766142]
> [   74.766142] other info that might help us debug this:
> [   74.766701]  Possible unsafe locking scenario:
> [   74.766701]
> [   74.767216]        CPU0
> [   74.767437]        ----
> [   74.767656]   lock(direct_mutex);
> [   74.767952]   lock(direct_mutex);
> [   74.768245]
> [   74.768245]  *** DEADLOCK ***
> [   74.768245]
> [   74.768750]  May be due to missing lock nesting notation
> [   74.768750]
> [   74.769332] 1 lock held by event-sample-fn/1084:
> [   74.769731]  #0: ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \
>     modify_ftrace_direct+0x34/0x1f0
> [   74.770496]
> [   74.770496] stack backtrace:
> [   74.770884] CPU: 4 PID: 1084 Comm: event-sample-fn Not tainted ...
> [   74.771498] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), ...
> [   74.772474] Call Trace:
> [   74.772696]  <TASK>
> [   74.772896]  dump_stack_lvl+0x44/0x5b
> [   74.773223]  __lock_acquire.cold.74+0xac/0x2b7
> [   74.773616]  lock_acquire+0xd2/0x310
> [   74.773936]  ? register_ftrace_function+0x1f/0x180
> [   74.774357]  ? lock_is_held_type+0xd8/0x130
> [   74.774744]  ? my_tramp2+0x11/0x11 [ftrace_direct_modify]
> [   74.775213]  __mutex_lock+0x99/0x1010
> [   74.775536]  ? register_ftrace_function+0x1f/0x180
> [   74.775954]  ? slab_free_freelist_hook.isra.43+0x115/0x160
> [   74.776424]  ? ftrace_set_hash+0x195/0x220
> [   74.776779]  ? register_ftrace_function+0x1f/0x180
> [   74.777194]  ? kfree+0x3e1/0x440
> [   74.777482]  ? my_tramp2+0x11/0x11 [ftrace_direct_modify]
> [   74.777941]  ? __schedule+0xb40/0xb40
> [   74.778258]  ? register_ftrace_function+0x1f/0x180
> [   74.778672]  ? my_tramp1+0xf/0xf [ftrace_direct_modify]
> [   74.779128]  register_ftrace_function+0x1f/0x180
> [   74.779527]  ? ftrace_set_filter_ip+0x33/0x70
> [   74.779910]  ? __schedule+0xb40/0xb40
> [   74.780231]  ? my_tramp1+0xf/0xf [ftrace_direct_modify]
> [   74.780678]  ? my_tramp2+0x11/0x11 [ftrace_direct_modify]
> [   74.781147]  ftrace_modify_direct_caller+0x5b/0x90
> [   74.781563]  ? 0xffffffffa0201000
> [   74.781859]  ? my_tramp1+0xf/0xf [ftrace_direct_modify]
> [   74.782309]  modify_ftrace_direct+0x1b2/0x1f0
> [   74.782690]  ? __schedule+0xb40/0xb40
> [   74.783014]  ? simple_thread+0x2a/0xb0 [ftrace_direct_modify]
> [   74.783508]  ? __schedule+0xb40/0xb40
> [   74.783832]  ? my_tramp2+0x11/0x11 [ftrace_direct_modify]
> [   74.784294]  simple_thread+0x76/0xb0 [ftrace_direct_modify]
> [   74.784766]  kthread+0xf5/0x120
> [   74.785052]  ? kthread_complete_and_exit+0x20/0x20
> [   74.785464]  ret_from_fork+0x22/0x30
> [   74.785781]  </TASK>
>
> Fix this by using register_ftrace_function_nolock in
> ftrace_modify_direct_caller.
>
> Fixes: 53cd885bc5c3 ("ftrace: Allow IPMODIFY and DIRECT ops on the same function")
> Reported-and-tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> Signed-off-by: Song Liu <song@kernel.org>
> ---
>  kernel/trace/ftrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 439e2ab6905e..d308d0674805 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5461,7 +5461,7 @@ int __weak ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
>         if (ret)
>                 goto out_lock;
>
> -       ret = register_ftrace_function(&stub_ops);
> +       ret = register_ftrace_function_nolock(&stub_ops);
>         if (ret) {
>                 ftrace_set_filter_ip(&stub_ops, ip, 1, 0);
>                 goto out_lock;
> --
> 2.30.2
>