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, edumazet@google.com,
jannh@google.com, netdev@vger.kernel.org, kernel-team@fb.com,
Waiman Long <longman@redhat.com>
Subject: Re: [PATCH bpf-next 2/4] bpf: fix lockdep false positive in stackmap
Date: Wed, 30 Jan 2019 20:44:07 +0100 [thread overview]
Message-ID: <20190130194407.GA3085@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190130193040.3hmh6g7efk5z3g2j@ast-mbp.dhcp.thefacebook.com>
On Wed, Jan 30, 2019 at 11:30:41AM -0800, Alexei Starovoitov wrote:
> On Wed, Jan 30, 2019 at 11:15:30AM +0100, Peter Zijlstra wrote:
> > On Tue, Jan 29, 2019 at 08:04:56PM -0800, Alexei Starovoitov wrote:
> > > Lockdep warns about false positive:
> >
> > This is not a false positive, and you probably also need to use
> > down_read_non_owner() to match this up_read_non_owner().
> >
> > {up,down}_read() and {up,down}_read_non_owner() are not only different
> > in the lockdep annotation; there is also optimistic spin stuff that
> > relies on 'owner' tracking.
>
> Can you point out in the code the spin bit?
Hurmph, looks like you're right. I got lost in that stuff again. I hate
that rwsem code :/
Rewriting that all is on the todo list somewhere, but it's far down :/
> As far as I can see sem->owner is debug only feature.
> All owner checks are done under CONFIG_DEBUG_RWSEMS.
>
> Also there is no down_read_trylock_non_owner() at the moment.
> We can argue about it for -next, but I'd rather silence lockdep
> with this patch today.
I don't agree with calling is silencing; it fixes an mis-use of the API.
But yes, keep the patch as is for now.
next prev parent reply other threads:[~2019-01-30 19:44 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 [this message]
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
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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