From: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public•gmane.org>
To: Alexei Starovoitov <ast-uqk4Ao+rVK5Wk0Htik3J/w@public•gmane.org>
Cc: Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public•gmane.org>,
Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public•gmane.org>,
Namhyung Kim <namhyung-DgEjT+Ai2ygdnm+yROfE0A@public•gmane.org>,
Arnaldo Carvalho de Melo
<acme-wEGCiKHe2LqWVfeAwA7xHQ@public•gmane.org>,
Jiri Olsa <jolsa-H+wXaHxf7aLQT0dZR+AlfA@public•gmane.org>,
Masami Hiramatsu
<masami.hiramatsu.pt-FCd8Q96Dh0JBDgjK7y7TUQ@public•gmane.org>,
"David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public•gmane.org>,
Daniel Borkmann <daniel-FeC+5ew28dpmcu3hnIyYJQ@public•gmane.org>,
linux-api-u79uwXL29TY76Z2rM5mHXA@public•gmane.org,
netdev-u79uwXL29TY76Z2rM5mHXA@public•gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public•gmane.org
Subject: Re: [PATCH v6 tip 2/8] tracing: attach BPF programs to kprobes
Date: Thu, 12 Mar 2015 16:15:07 +0100 [thread overview]
Message-ID: <20150312151507.GI2896@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <1426047534-8148-3-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
On Tue, Mar 10, 2015 at 09:18:48PM -0700, Alexei Starovoitov wrote:
> +unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
> +{
> + unsigned int ret;
> + int cpu;
> +
> + if (in_nmi()) /* not supported yet */
> + return 1;
> +
> + preempt_disable_notrace();
> +
> + cpu = raw_smp_processor_id();
> + if (unlikely(per_cpu(bpf_prog_active, cpu)++ != 0)) {
> + /* since some bpf program is already running on this cpu,
> + * don't call into another bpf program (same or different)
> + * and don't send kprobe event into ring-buffer,
> + * so return zero here
> + */
> + ret = 0;
> + goto out;
> + }
> +
> + rcu_read_lock();
You've so far tried very hard to not get into tracing; and then you call
rcu_read_lock() :-)
So either document why this isn't a problem, provide
rcu_read_lock_notrace() or switch to RCU-sched and thereby avoid the
problem.
> + ret = BPF_PROG_RUN(prog, ctx);
> + rcu_read_unlock();
> +
> + out:
> + per_cpu(bpf_prog_active, cpu)--;
> + preempt_enable_notrace();
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(trace_call_bpf);
next prev parent reply other threads:[~2015-03-12 15:15 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-11 4:18 [PATCH v6 tip 0/8] tracing: attach eBPF programs to kprobes Alexei Starovoitov
2015-03-11 4:18 ` [PATCH v6 tip 1/8] bpf: make internal bpf API independent of CONFIG_BPF_SYSCALL ifdefs Alexei Starovoitov
2015-03-11 4:18 ` [PATCH v6 tip 2/8] tracing: attach BPF programs to kprobes Alexei Starovoitov
[not found] ` <1426047534-8148-3-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-12 15:15 ` Peter Zijlstra [this message]
2015-03-12 16:18 ` Alexei Starovoitov
2015-03-12 16:23 ` Steven Rostedt
2015-03-12 16:43 ` Alexei Starovoitov
[not found] ` <5501C24A.30206-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-12 16:47 ` Steven Rostedt
2015-03-11 4:18 ` [PATCH v6 tip 3/8] tracing: allow BPF programs to call bpf_ktime_get_ns() Alexei Starovoitov
[not found] ` <1426047534-8148-4-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-13 11:24 ` He Kuang
[not found] ` <5502C8EB.9070307-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2015-03-13 16:38 ` Alexei Starovoitov
2015-03-11 4:18 ` [PATCH v6 tip 4/8] tracing: allow BPF programs to call bpf_trace_printk() Alexei Starovoitov
2015-03-11 4:18 ` [PATCH v6 tip 5/8] samples: bpf: simple non-portable kprobe filter example Alexei Starovoitov
2015-03-11 4:18 ` [PATCH v6 tip 6/8] samples: bpf: counting example for kfree_skb and write syscall Alexei Starovoitov
[not found] ` <1426047534-8148-1-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
2015-03-11 4:18 ` [PATCH v6 tip 7/8] samples: bpf: IO latency analysis (iosnoop/heatmap) Alexei Starovoitov
2015-03-11 4:18 ` [PATCH v6 tip 8/8] samples: bpf: kmem_alloc/free tracker Alexei Starovoitov
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