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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id m59sm2603015qtd.46.2020.05.14.06.44.28 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 May 2020 06:44:28 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.80.23.2.2\)) Subject: Re: Default enable RCU list lockdep debugging with PROVE_RCU From: Qian Cai In-Reply-To: <20200514133328.GG2869@paulmck-ThinkPad-P72> Date: Thu, 14 May 2020 09:44:28 -0400 Cc: Stephen Rothwell , Linux Next Mailing List , Linux Kernel Mailing List , Madhuparna Bhowmik , Amol Grover , Dmitry Vyukov Content-Transfer-Encoding: quoted-printable Message-Id: References: <20200514222535.259cb69e@canb.auug.org.au> <20200514133328.GG2869@paulmck-ThinkPad-P72> To: "Paul E. McKenney" X-Mailer: Apple Mail (2.3608.80.23.2.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On May 14, 2020, at 9:33 AM, Paul E. McKenney = 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 = 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?=