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 11:10:58 +0100 [thread overview]
Message-ID: <20190130101058.GD2278@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190130040458.2544340-4-ast@kernel.org>
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();
_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 10:11 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 [this message]
2019-01-30 10:37 ` Peter Zijlstra
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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