From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andrii Nakryiko <andriin@fb.com>,
Alan Stern <stern@rowland.harvard.edu>,
parri.andrea@gmail.com, will@kernel.org, boqun.feng@gmail.com,
npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk,
luc.maranget@inria.fr, akiyks@gmail.com, dlustig@nvidia.com,
joel@joelfernandes.org, linux-kernel@vger.kernel.org,
linux-arch@vger.kernel.org,
"andrii.nakryiko@gmail.com" <andrii.nakryiko@gmail.com>
Subject: Re: Some -serious- BPF-related litmus tests
Date: Mon, 25 May 2020 08:47:30 -0700 [thread overview]
Message-ID: <20200525154730.GW2869@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200525112521.GD317569@hirez.programming.kicks-ass.net>
On Mon, May 25, 2020 at 01:25:21PM +0200, Peter Zijlstra wrote:
> On Fri, May 22, 2020 at 12:38:21PM -0700, Andrii Nakryiko wrote:
> > On 5/22/20 10:43 AM, Paul E. McKenney wrote:
> > > On Fri, May 22, 2020 at 10:32:01AM -0400, Alan Stern wrote:
>
> > > > Also, what use is a spinlock that is accessed in only one thread?
> > >
> > > Multiple writers synchronize via the spinlock in this case. I am
> > > guessing that his larger 16-hour test contended this spinlock.
> >
> > Yes, spinlock is for coordinating multiple producers. 2p1c cases (bounded
> > and unbounded) rely on this already. 1p1c cases are sort of subsets (but
> > very fast to verify) checking only consumer/producer interaction.
>
> Does that spinlock imply that we can now never fix that atrocious
> bpf_prog_active trainwreck ?
>
> How does that spinlock not trigger the USED <- IN-NMI lockdep check:
>
> f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions")
>
> ?
>
> That is; how can you use a spinlock on the producer side at all?
So even trylock is now forbidden in NMI handlers? If so, why?
Thanx, Paul
next prev parent reply other threads:[~2020-05-25 15:47 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-22 0:38 Some -serious- BPF-related litmus tests Paul E. McKenney
2020-05-22 9:44 ` Peter Zijlstra
2020-05-22 10:56 ` Paul E. McKenney
2020-05-22 14:36 ` Alan Stern
2020-05-22 17:45 ` Paul E. McKenney
2020-05-22 14:32 ` Alan Stern
2020-05-22 14:32 ` Alan Stern
2020-05-22 17:43 ` Paul E. McKenney
2020-05-22 17:43 ` Paul E. McKenney
2020-05-22 19:38 ` Andrii Nakryiko
2020-05-24 12:09 ` Akira Yokosawa
2020-05-24 12:09 ` Akira Yokosawa
2020-05-25 18:31 ` Andrii Nakryiko
2020-05-25 22:01 ` Akira Yokosawa
2020-05-25 23:31 ` Andrii Nakryiko
2020-05-26 10:50 ` Akira Yokosawa
2020-05-26 14:02 ` Akira Yokosawa
2020-05-26 20:19 ` Andrii Nakryiko
2020-05-26 23:00 ` Akira Yokosawa
2020-05-27 0:09 ` Andrii Nakryiko
2020-05-26 20:15 ` Andrii Nakryiko
2020-05-26 22:23 ` Akira Yokosawa
2020-05-25 11:25 ` Peter Zijlstra
2020-05-25 15:47 ` Paul E. McKenney [this message]
2020-05-25 15:47 ` Paul E. McKenney
2020-05-25 17:02 ` Peter Zijlstra
2020-05-25 17:21 ` Paul E. McKenney
2020-05-25 17:45 ` Paul E. McKenney
2020-05-28 22:00 ` Joel Fernandes
2020-05-28 22:16 ` Peter Zijlstra
2020-05-29 5:14 ` Andrii Nakryiko
2020-05-29 12:36 ` Peter Zijlstra
2020-05-29 20:01 ` Andrii Nakryiko
2020-05-29 20:53 ` Peter Zijlstra
2020-05-25 14:53 ` Boqun Feng
2020-05-25 14:53 ` Boqun Feng
2020-05-25 18:38 ` Andrii Nakryiko
2020-05-28 21:48 ` Joel Fernandes
2020-05-29 4:38 ` Andrii Nakryiko
2020-05-29 4:38 ` Andrii Nakryiko
2020-05-29 17:23 ` Joel Fernandes
2020-05-29 20:10 ` Andrii Nakryiko
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