From: Yonghong Song <yhs@meta.com>
To: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>
Cc: bpf@vger.kernel.org, Martin KaFai Lau <kafai@fb.com>,
Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Florent Revest <revest@chromium.org>
Subject: Re: [PATCHv3 bpf-next 2/3] bpf: Do cleanup in bpf_bprintf_cleanup only when needed
Date: Fri, 16 Dec 2022 16:25:47 -0800 [thread overview]
Message-ID: <e87a43b3-3b8c-cd23-6563-9525f51982c2@meta.com> (raw)
In-Reply-To: <20221215214430.1336195-3-jolsa@kernel.org>
On 12/15/22 1:44 PM, Jiri Olsa wrote:
> Currently we always cleanup/decrement bpf_bprintf_nest_level
> variable in bpf_bprintf_cleanup if it's > 0.
>
> There's possible scenario where this could cause a problem,
> when bpf_bprintf_prepare does not get bin_args buffer (because
> num_args is 0) and following bpf_bprintf_cleanup call decrements
> bpf_bprintf_nest_level variable, like:
>
> in task context:
> bpf_bprintf_prepare(num_args != 0) increments 'bpf_bprintf_nest_level = 1'
> -> first irq :
> bpf_bprintf_prepare(num_args == 0)
> bpf_bprintf_cleanup decrements 'bpf_bprintf_nest_level = 0'
> -> second irq:
> bpf_bprintf_prepare(num_args != 0) bpf_bprintf_nest_level = 1
> gets same buffer as task context above
>
> Adding check to bpf_bprintf_cleanup and doing the real cleanup
> only if we got bin_args data in the first place.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
next prev parent reply other threads:[~2022-12-17 0:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-15 21:44 [PATCHv3 bpf-next 0/3] bpf: Get rid of trace_printk_lock Jiri Olsa
2022-12-15 21:44 ` [PATCHv3 bpf-next 1/3] bpf: Add struct for bin_args arg in bpf_bprintf_prepare Jiri Olsa
2022-12-17 0:25 ` Yonghong Song
2022-12-15 21:44 ` [PATCHv3 bpf-next 2/3] bpf: Do cleanup in bpf_bprintf_cleanup only when needed Jiri Olsa
2022-12-17 0:25 ` Yonghong Song [this message]
2022-12-15 21:44 ` [PATCHv3 bpf-next 3/3] bpf: Remove trace_printk_lock Jiri Olsa
2022-12-17 0:28 ` Yonghong Song
2022-12-19 21:10 ` [PATCHv3 bpf-next 0/3] bpf: Get rid of trace_printk_lock patchwork-bot+netdevbpf
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