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Date:   Fri, 09 Sep 2022 23:43:39 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Subject: Re: [PATCH v5 bpf-next 2/4] ftrace: Allow IPMODIFY and DIRECT ops on
 the same function
To:     Song Liu <songliubraving@fb.com>
Cc:     Kernel Team <Kernel-team@fb.com>, bpf <bpf@vger.kernel.org>,
        "daniel@iogearbox.net" <daniel@iogearbox.net>,
        "jolsa@kernel.org" <jolsa@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "live-patching@vger.kernel.org" <live-patching@vger.kernel.org>,
        "rostedt@goodmis.org" <rostedt@goodmis.org>,
        Song Liu <song@kernel.org>
References: <20220720002126.803253-1-song@kernel.org>
        <20220720002126.803253-3-song@kernel.org>
        <1662724350.8os86rhyxk.naveen@linux.ibm.com>
        <B59F0FD0-FA3E-4A8B-B588-8F9AA8AC602A@fb.com>
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Hi Song,

Song Liu wrote:
>=20
>=20
>> On Sep 9, 2022, at 4:58 AM, Naveen N. Rao <naveen.n.rao@linux.ibm.com> w=
rote:
>>=20
>> Song Liu wrote:
>=20
> [...]
>=20
>>> +
>>> /**
>>>  * register_ftrace_function - register a function for profiling
>>>  * @ops:	ops structure that holds the function for profiling.
>>> @@ -8018,14 +8206,15 @@ int register_ftrace_function(struct ftrace_ops =
*ops)
>>> {
>>> 	int ret;
>>> -	ftrace_ops_init(ops);
>>> -
>>> -	mutex_lock(&ftrace_lock);
>>> -
>>> -	ret =3D ftrace_startup(ops, 0);
>>> +	lock_direct_mutex();
>>=20
>> Trying to enable ftrace direct on powerpc, this is resulting in a hung t=
ask when testing samples/ftrace/ftrace-direct-modify.c
>>=20
>> Essentially, the sample calls modify_ftrace_direct(), which grabs direct=
_mutex before calling ftrace_modify_direct_caller()->register_ftrace_functi=
on().
>>=20
>=20
> Thanks for the report. Would the following change fix the issue?
>=20
> Song
>=20
> diff --git i/kernel/trace/ftrace.c w/kernel/trace/ftrace.c
> index bc921a3f7ea8..2f1e6cfa834e 100644
> --- i/kernel/trace/ftrace.c
> +++ w/kernel/trace/ftrace.c
> @@ -5496,7 +5496,7 @@ int __weak ftrace_modify_direct_caller(struct ftrac=
e_func_entry *entry,
>         if (ret)
>                 goto out_lock;
>=20
> -       ret =3D register_ftrace_function(&stub_ops);
> +       ret =3D register_ftrace_function_nolock(&stub_ops);
>         if (ret) {
>                 ftrace_set_filter_ip(&stub_ops, ip, 1, 0);
>                 goto out_lock;
>=20

That fixes it for me.
Reported-and-Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>


Thanks!
- Naveen