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From: Peter Zijlstra <peterz@infradead.org>
To: Andrii Nakryiko <andriin@fb.com>
Cc: paulmck@kernel.org, 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 13:25:21 +0200	[thread overview]
Message-ID: <20200525112521.GD317569@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <006e2bc6-7516-1584-3d8c-e253211c157e@fb.com>

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?

  parent reply	other threads:[~2020-05-25 11:25 UTC|newest]

Thread overview: 37+ 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 17:43     ` Paul E. McKenney
2020-05-22 19:38       ` Andrii Nakryiko
2020-05-22 19:38         ` Andrii Nakryiko
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 [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 18:38           ` Andrii Nakryiko
2020-05-28 21:48             ` Joel Fernandes
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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