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McKenney" , Paolo Bonzini , Joel Fernandes Subject: Re: [PATCH 2/3] rcu: Equip sleepable RCU with lockdep dependency graph checks Message-ID: References: <20230113065955.815667-1-boqun.feng@gmail.com> <20230113130330.1027-1-hdanton@sina.com> <20230113235809.1085-1-hdanton@sina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230113235809.1085-1-hdanton@sina.com> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: hzj1n9i8p1qzmdfqkoqt1huux3ioepd8 X-Rspamd-Queue-Id: 370851C000E X-HE-Tag: 1673655489-814952 X-HE-Meta: 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 xjf0JalH XNlLbikWAwwKvCUN3ijC1BqIfJ1lAruviW+h/7+zb1LvJI3FPrLJRsERTeN2Zkosgcg2lqurQU1KxBsnS4+iecRthWrXO56meAPVRTQMVH43vlwF62wwqzDF8Jg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Jan 14, 2023 at 07:58:09AM +0800, Hillf Danton wrote: > On 13 Jan 2023 09:58:10 -0800 Boqun Feng > > On Fri, Jan 13, 2023 at 09:03:30PM +0800, Hillf Danton wrote: > > > On 12 Jan 2023 22:59:54 -0800 Boqun Feng > > > > --- a/kernel/rcu/srcutree.c > > > > +++ b/kernel/rcu/srcutree.c > > > > @@ -1267,6 +1267,8 @@ static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm) > > > > { > > > > struct rcu_synchronize rcu; > > > > > > > > + srcu_lock_sync(&ssp->dep_map); > > > > + > > > > RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || > > > > lock_is_held(&rcu_bh_lock_map) || > > > > lock_is_held(&rcu_lock_map) || > > > > -- > > > > 2.38.1 > > > > > > The following deadlock is able to escape srcu_lock_sync() because the > > > __lock_release folded in sync leaves one lock on the sync side. > > > > > > cpu9 cpu0 > > > --- --- > > > lock A srcu_lock_acquire(&ssp->dep_map); > > > srcu_lock_sync(&ssp->dep_map); > > > lock A > > > > But isn't it just the srcu_mutex_ABBA test case in patch #3, and my run > > of lockdep selftest shows we can catch it. Anything subtle I'm missing? > > I am leaning to not call it ABBA deadlock, because B is unlocked. > > task X task Y > --- --- > lock A > lock B > lock B > unlock B > wait_for_completion E > > lock A > complete E > > And no deadlock should be detected/caught after B goes home. Your example makes me more confused.. given the case: task X task Y --- --- mutex_lock(A); srcu_read_lock(B); synchronze_srcu(B); mutex_lock(A); isn't it a deadlock? If your example, A, B or E which one is srcu? Regards, Boqun