linux-kernel - Re: [PATCH v2 1/1] bpf: Drop unprotected find_vpid() in favour of find_get

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Message-ID: <YvIDu0zU7eDUGEYq@google.com>
Date:   Tue, 9 Aug 2022 07:50:35 +0100
From:   Lee Jones <lee@...nel.org>
To:     Jiri Olsa <olsajiri@...il.com>
Cc:     linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, bpf@...r.kernel.org
Subject: Re: [PATCH v2 1/1] bpf: Drop unprotected find_vpid() in favour of
 find_get_pid()

On Wed, 03 Aug 2022, Jiri Olsa wrote:

> On Wed, Aug 03, 2022 at 02:48:21PM +0100, Lee Jones wrote:
> > The documentation for find_pid() clearly states:
> 
> nit: typo find_vpid

Sorry missed this.

Will fix.

> >   "Must be called with the tasklist_lock or rcu_read_lock() held."
> > 
> > Presently we do neither.
> > 
> > Let's use find_get_pid() which searches for the vpid, then takes a
> > reference to it preventing early free, all within the safety of
> > rcu_read_lock().  Once we have our reference we can safely make use of
> > it up until the point it is put.
> > 
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: John Fastabend <john.fastabend@...il.com>
> > Cc: Andrii Nakryiko <andrii@...nel.org>
> > Cc: Martin KaFai Lau <martin.lau@...ux.dev>
> > Cc: Song Liu <song@...nel.org>
> > Cc: Yonghong Song <yhs@...com>
> > Cc: KP Singh <kpsingh@...nel.org>
> > Cc: Stanislav Fomichev <sdf@...gle.com>
> > Cc: Hao Luo <haoluo@...gle.com>
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > Cc: bpf@...r.kernel.org
> > Fixes: 41bdc4b40ed6f ("bpf: introduce bpf subcommand BPF_TASK_FD_QUERY")
> > Signed-off-by: Lee Jones <lee@...nel.org>
> 
> Acked-by: Jiri Olsa <jolsa@...nel.org>

Thanks.

-- 
Lee Jones [李琼斯]