From: Peter Zijlstra <peterz@infradead•org>
To: Alexei Starovoitov <ast@kernel•org>
Cc: davem@davemloft•net, daniel@iogearbox•net, edumazet@google•com,
jannh@google•com, netdev@vger•kernel.org, kernel-team@fb•com
Subject: Re: [PATCH bpf-next 3/4] bpf: fix lockdep false positive in bpf_prog_register
Date: Wed, 30 Jan 2019 11:37:54 +0100 [thread overview]
Message-ID: <20190130103754.GA3103@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190130101058.GD2278@hirez.programming.kicks-ass.net>
On Wed, Jan 30, 2019 at 11:10:58AM +0100, Peter Zijlstra wrote:
> On Tue, Jan 29, 2019 at 08:04:57PM -0800, Alexei Starovoitov wrote:
> > Lockdep warns about false positive:
>
> The report reads like:
>
> tracepoint_probe_register()
> #0 mutex_lock(&tracepoint_mutex)
> tracepoint_add_func()
> static_key_slow_inc()
> #1 cpus_read_lock();
>
>
> _cpu_up()
> #1 cpus_write_lock();
> ...
> perf_event_init_cpu()
> #2 mutex_lock(&pmus_lock);
> #3 mutex_lock(&ctx->mutex);
>
>
> perf_ioctl()
> #4 perf_event_ctx_lock();
Sorry, that's #3, and then do s/#5/#4/ on the rest of the text.
> _perf_ioctl(IOC_QUERY_BPF)
> perf_event_query_prog_array()
> #5 mutex_lock(&bpf_event_mutex);
>
>
> bpf_probe_register()
> #5 mutex_lock(&bpf_event_mutex);
> __bpf_probe_register()
> tracepoint_probe_register()
> #0 mutex_lock(&tracepoint_mutex);
>
> Which to me reads like an entirely valid deadlock scenario.
>
> And note that the first and last can be combined to give:
>
> bpf_probe_register()
> #5 mutex_lock(&bpf_event_mutex);
> __bpf_probe_register()
> tracepoint_probe_register()
> #0 mutex_lock(&tracepoint_mutex);
> tracepoint_add_func()
> static_key_slow_inc()
> #1 cpus_read_lock();
>
>
> Which generates a deadlock even without #0.
>
> Why do you say this is not possible? All you need is 3 CPUs, one doing a
> CPU online, one doing a perf ioctl() and one doing that
> bpf_probe_register().
>
>
next prev parent reply other threads:[~2019-01-30 10:38 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-30 4:04 [PATCH bpf-next 0/4] bpf: fixes for lockdep and deadlock Alexei Starovoitov
2019-01-30 4:04 ` [PATCH bpf-next 1/4] bpf: fix lockdep false positive in percpu_freelist Alexei Starovoitov
2019-01-30 10:21 ` Peter Zijlstra
2019-01-30 19:27 ` Alexei Starovoitov
2019-01-30 19:53 ` Peter Zijlstra
2019-01-30 20:18 ` Alexei Starovoitov
2019-01-30 4:04 ` [PATCH bpf-next 2/4] bpf: fix lockdep false positive in stackmap Alexei Starovoitov
2019-01-30 10:15 ` Peter Zijlstra
2019-01-30 19:30 ` Alexei Starovoitov
2019-01-30 19:42 ` Waiman Long
2019-01-30 20:10 ` Alexei Starovoitov
2019-01-30 21:11 ` Waiman Long
2019-01-30 21:32 ` Waiman Long
2019-01-31 2:01 ` Alexei Starovoitov
2019-01-31 2:48 ` Waiman Long
2019-02-06 3:21 ` Eric Dumazet
2019-02-06 3:30 ` Alexei Starovoitov
2019-02-06 3:40 ` Eric Dumazet
2019-01-30 19:44 ` Peter Zijlstra
2019-01-30 20:05 ` Waiman Long
2019-01-30 4:04 ` [PATCH bpf-next 3/4] bpf: fix lockdep false positive in bpf_prog_register Alexei Starovoitov
2019-01-30 10:10 ` Peter Zijlstra
2019-01-30 10:37 ` Peter Zijlstra [this message]
2019-01-30 19:32 ` Alexei Starovoitov
2019-01-30 19:46 ` Peter Zijlstra
2019-01-30 4:04 ` [PATCH bpf-next 4/4] bpf: Fix syscall's stackmap lookup potential deadlock Alexei Starovoitov
2019-01-30 4:07 ` [PATCH bpf-next 0/4] bpf: fixes for lockdep and deadlock Alexei Starovoitov
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