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Subject: Re: Default enable RCU list lockdep debugging with PROVE_RCU
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <20200514133328.GG2869@paulmck-ThinkPad-P72>
Date:   Thu, 14 May 2020 09:44:28 -0400
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
        Amol Grover <frextrite@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>
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References: <20200514222535.259cb69e@canb.auug.org.au>
 <ADC503BE-32C0-46BB-A65E-59FFEC30ED57@lca.pw>
 <20200514133328.GG2869@paulmck-ThinkPad-P72>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On May 14, 2020, at 9:33 AM, Paul E. McKenney <paulmck@kernel.org> =
wrote:
>=20
> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
>>=20
>>=20
>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell <sfr@canb.auug.org.au> =
wrote:
>>>=20
>>> Hi Paul,
>>>=20
>>> This patch in the rcu tree
>>>=20
>>> d13fee049fa8 ("Default enable RCU list lockdep debugging with =
PROVE_RCU")
>>>=20
>>> is causing whack-a-mole in the syzbot testing of linux-next.  =
Because
>>> they always do a debug build of linux-next, no testing is getting =
done. :-(
>>>=20
>>> Can we find another way to find all the bugs that are being =
discovered
>>> (very slowly)?
>>=20
>> Alternatively, could syzbot to use PROVE_RCU=3Dn temporarily because =
it can=E2=80=99t keep up with it? I personally found PROVE_RCU_LIST=3Dy =
is still useful for my linux-next testing, and don=E2=80=99t want to =
lose that coverage overnight.
>=20
> The problem is that PROVE_RCU is exactly PROVE_LOCKING, and asking =
people
> to test without PROVE_LOCKING is a no-go in my opinion.  But of course
> on the other hand if there is no testing of RCU list lockdep =
debugging,
> those issues will never be found, let alone fixed.
>=20
> One approach would be to do as Stephen asks (either remove =
d13fee049fa8
> or pull it out of -next) and have testers force-enable the RCU list
> lockdep debugging.
>=20
> Would that work for you?

Alternatively, how about having

PROVE_RCU_LIST=3Dn if DEBUG_AID_FOR_SYZBOT

since it is only syzbot can=E2=80=99t keep up with it?=