linux-kernel - Re: [PATCH net-next 1/9] bpf: prevent kprobe+bpf deadlocks

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Message-ID: <56DD52F0.1060604@iogearbox.net>
Date:	Mon, 07 Mar 2016 11:07:44 +0100
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Alexei Starovoitov <ast@...com>,
	"David S . Miller" <davem@...emloft.net>
CC:	Daniel Wagner <daniel.wagner@...-carit.de>,
	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	Wang Nan <wangnan0@...wei.com>, He Kuang <hekuang@...wei.com>,
	Martin KaFai Lau <kafai@...com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...com
Subject: Re: [PATCH net-next 1/9] bpf: prevent kprobe+bpf deadlocks

On 03/07/2016 02:58 AM, Alexei Starovoitov wrote:
> if kprobe is placed within update or delete hash map helpers
> that hold bucket spin lock and triggered bpf program is trying to
> grab the spinlock for the same bucket on the same cpu, it will
> deadlock.
> Fix it by extending existing recursion prevention mechanism.
>
> Note, map_lookup and other tracing helpers don't have this problem,
> since they don't hold any locks and don't modify global data.
> bpf_trace_printk has its own recursive check and ok as well.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

LGTM

Acked-by: Daniel Borkmann <daniel@...earbox.net>