From: Peter Zijlstra <peterz@infradead•org>
To: Alexei Starovoitov <alexei.starovoitov@gmail•com>
Cc: Alexei Starovoitov <ast@kernel•org>,
davem@davemloft•net, daniel@iogearbox•net,
jakub.kicinski@netronome•com, netdev@vger•kernel.org,
kernel-team@fb•com, mingo@redhat•com, will.deacon@arm•com,
Paul McKenney <paulmck@linux•vnet.ibm.com>,
jannh@google•com
Subject: Re: [PATCH v4 bpf-next 1/9] bpf: introduce bpf_spin_lock
Date: Mon, 28 Jan 2019 09:43:10 +0100 [thread overview]
Message-ID: <20190128084310.GC28467@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190125234241.soomtkrgp2i7m7ul@ast-mbp.dhcp.thefacebook.com>
On Fri, Jan 25, 2019 at 03:42:43PM -0800, Alexei Starovoitov wrote:
> On Fri, Jan 25, 2019 at 10:10:57AM +0100, Peter Zijlstra wrote:
> > What about the progs that run from SoftIRQ ? Since that bpf_prog_active
> > thing isn't inside BPF_PROG_RUN() what is to stop say:
> >
> > reuseport_select_sock()
> > ...
> > BPF_PROG_RUN()
> > bpf_spin_lock()
> > <IRQ>
> > ...
> > BPF_PROG_RUN()
> > bpf_spin_lock() // forever more
> >
> > </IRQ>
> >
> > Unless you stick that bpf_prog_active stuff inside BPF_PROG_RUN itself,
> > I don't see how you can fundamentally avoid this happening (now or in
> > the future).
> But your issue above is valid.
> We don't use bpf_prog_active for networking progs, since we allow
> for one level of nesting due to the classic SKF_AD_PAY_OFFSET legacy.
> Also we allow tracing progs to nest with networking progs.
> People using this actively.
> Typically it's not an issue, since in networking there is no
> arbitrary nesting (unlike kprobe/nmi in tracing),
> but for bpf_spin_lock it can be, since the same map can be shared
> by networking and tracing progs and above deadlock would be possible:
> (first BPF_PROG_RUN will be from networking prog, then kprobe+bpf's
> BPF_PROG_RUN accessing the same map with bpf_spin_lock)
>
> So for now I'm going to allow bpf_spin_lock in networking progs only,
> since there is no arbitrary nesting there.
Isn't that still broken? AFAIU networking progs can happen in task
context (TX) and SoftIRQ context (RX), which can nest.
> And once we figure out the safety concerns for kprobe/tracepoint progs
> we can enable bpf_spin_lock there too.
> NMI bpf progs will never have bpf_spin_lock.
kprobe is like NMI, since it pokes an INT3 instruction which can trigger
in the middle of IRQ-disabled or even in NMIs. Similar arguments can be
made for tracepoints, they can happen 'anywhere'.
next prev parent reply other threads:[~2019-01-28 8:43 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-24 4:13 [PATCH v4 bpf-next 0/9] introduce bpf_spin_lock Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 1/9] bpf: " Alexei Starovoitov
2019-01-24 18:01 ` Peter Zijlstra
2019-01-24 18:56 ` Peter Zijlstra
2019-01-24 23:42 ` Paul E. McKenney
2019-01-25 0:05 ` Alexei Starovoitov
2019-01-25 1:22 ` Paul E. McKenney
2019-01-25 1:46 ` Jann Horn
2019-01-25 2:38 ` Alexei Starovoitov
2019-01-25 4:27 ` Alexei Starovoitov
2019-01-25 4:31 ` Paul E. McKenney
2019-01-25 4:47 ` Alexei Starovoitov
2019-01-25 16:02 ` Paul E. McKenney
2019-01-25 4:11 ` Paul E. McKenney
2019-01-25 16:18 ` Jann Horn
2019-01-25 22:51 ` Paul E. McKenney
2019-01-25 23:44 ` Alexei Starovoitov
2019-01-26 0:43 ` Jann Horn
2019-01-26 0:59 ` Jann Horn
2019-01-24 23:58 ` Alexei Starovoitov
2019-01-25 0:18 ` Jann Horn
2019-01-25 2:49 ` Alexei Starovoitov
2019-01-25 2:29 ` Eric Dumazet
2019-01-25 2:34 ` Alexei Starovoitov
2019-01-25 2:44 ` Eric Dumazet
2019-01-25 2:57 ` Alexei Starovoitov
2019-01-25 8:38 ` Peter Zijlstra
2019-01-25 9:10 ` Peter Zijlstra
2019-01-25 23:42 ` Alexei Starovoitov
2019-01-28 8:24 ` Peter Zijlstra
2019-01-28 8:31 ` Peter Zijlstra
2019-01-28 8:35 ` Peter Zijlstra
2019-01-28 20:49 ` Alexei Starovoitov
2019-01-28 8:43 ` Peter Zijlstra [this message]
2019-01-28 21:37 ` Alexei Starovoitov
2019-01-29 8:59 ` Peter Zijlstra
2019-01-30 2:20 ` Alexei Starovoitov
2019-01-25 9:59 ` Peter Zijlstra
2019-01-25 10:09 ` Peter Zijlstra
2019-01-25 10:23 ` Peter Zijlstra
2019-01-26 0:17 ` bpf memory model. Was: " Alexei Starovoitov
2019-01-28 9:24 ` Peter Zijlstra
2019-01-28 21:56 ` Alexei Starovoitov
2019-01-29 9:16 ` Peter Zijlstra
2019-01-30 2:32 ` Alexei Starovoitov
2019-01-30 8:58 ` Peter Zijlstra
2019-01-30 19:36 ` Alexei Starovoitov
2019-01-30 18:11 ` Will Deacon
2019-01-30 18:36 ` Paul E. McKenney
2019-01-30 19:51 ` Alexei Starovoitov
2019-01-30 21:05 ` Paul E. McKenney
2019-01-30 22:57 ` Alexei Starovoitov
2019-01-31 14:01 ` Paul E. McKenney
2019-01-31 18:47 ` Alexei Starovoitov
2019-02-01 14:05 ` Paul E. McKenney
2019-01-30 19:50 ` Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 2/9] bpf: add support for bpf_spin_lock to cgroup local storage Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 3/9] tools/bpf: sync include/uapi/linux/bpf.h Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 4/9] selftests/bpf: add bpf_spin_lock tests Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 5/9] selftests/bpf: add bpf_spin_lock C test Alexei Starovoitov
2019-01-24 4:14 ` [PATCH v4 bpf-next 6/9] bpf: introduce BPF_F_LOCK flag Alexei Starovoitov
2019-01-24 4:14 ` [PATCH v4 bpf-next 7/9] tools/bpf: sync uapi/bpf.h Alexei Starovoitov
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