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Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion
From:   Qian Cai <cai@redhat.com>
To:     paulmck@kernel.org
Cc:     Boqun Feng <boqun.feng@gmail.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>, x86 <x86@kernel.org>,
        linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Date:   Wed, 28 Oct 2020 16:08:59 -0400
In-Reply-To: <20201028155328.GC3249@paulmck-ThinkPad-P72>
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On Wed, 2020-10-28 at 08:53 -0700, Paul E. McKenney wrote:
> On Wed, Oct 28, 2020 at 10:39:47AM -0400, Qian Cai wrote:
> > On Tue, 2020-10-27 at 20:01 -0700, Paul E. McKenney wrote:
> > > If I have the right email thread associated with the right fixes, these
> > > commits in -rcu should be what you are looking for:
> > > 
> > > 73b658b6b7d5 ("rcu: Prevent lockdep-RCU splats on lock
> > > acquisition/release")
> > > 626b79aa935a ("x86/smpboot:  Move rcu_cpu_starting() earlier")
> > > 
> > > And maybe this one as well:
> > > 
> > > 3a6f638cb95b ("rcu,ftrace: Fix ftrace recursion")
> > > 
> > > Please let me know if these commits do not fix things.
> > While those patches silence the warnings for x86. Other arches are still
> > suffering. It is only after applying the patch from Boqun below fixed
> > everything.
> 
> Fair point!
> 
> > Is it a good idea for Boqun to write a formal patch or we should fix all
> > arches
> > individually like "x86/smpboot: Move rcu_cpu_starting() earlier"?
> 
> By Boqun's patch, you mean the change to debug_lockdep_rcu_enabled()
> shown below?  Peter Zijlstra showed that real failures can happen, so we

Yes.

> do not want to cover them up.  So we are firmly in "fix all architectures"
> space here, sorry!
> 
> I am happy to accumulate those patches, but cannot commit to creating
> or testing them.

Okay, I posted 3 patches for each arch and CC'ed you. BTW, it looks like
something is wrong on @vger.kernel.org today where I received many of those,

4.7.1 Hello [216.205.24.124], for recipient address <linux-kernel@vger.kernel.org> the policy analysis reported: zpostgrey: connect: Connection refused

and I can see your previous mails did not even reach there either.

https://lore.kernel.org/lkml/