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[98.249.43.138]) by smtp.gmail.com with ESMTPSA id l17-20020ac848d1000000b003ab43dabfb1sm9206133qtr.55.2023.01.12.06.54.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Jan 2023 06:54:38 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Joel Fernandes Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v2] rcu: Fix the start_poll_synchronize_rcu_expedited() be invoked very early Date: Thu, 12 Jan 2023 09:54:26 -0500 Message-Id: <13E7FFFD-9F91-4221-B52C-E6CB1EFBC2AB@joelfernandes.org> References: <20230112075629.1661429-1-qiang1.zhang@intel.com> Cc: paulmck@kernel.org, frederic@kernel.org, quic_neeraju@quicinc.com, rcu@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230112075629.1661429-1-qiang1.zhang@intel.com> To: Zqiang X-Mailer: iPhone Mail (20B101) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jan 12, 2023, at 2:51 AM, Zqiang wrote: >=20 > =EF=BB=BFCurrently, the start_poll_synchronize_rcu_expedited() can be invo= ked > very early. before rcu_init(), the rcu_data structure's->mynode is not > initialized, if invoke start_poll_synchronize_rcu_expedited() before > rcu_init(), will trigger a null rcu_node structure's->exp_seq_poll access.= >=20 > This commit add boot_exp_seq_poll_rq member to rcu_state structure to > store seq number return by invoke start_poll_synchronize_rcu_expedited() > very early. >=20 > Fixes: d96c52fe4907 ("rcu: Add polled expedited grace-period primitives") > Signed-off-by: Zqiang Reviewed-by: Joel Fernandes (Google) Thanks. > --- > kernel/rcu/tree.c | 3 ++- > kernel/rcu/tree.h | 1 + > kernel/rcu/tree_exp.h | 6 ++++-- > 3 files changed, 7 insertions(+), 3 deletions(-) >=20 > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 63545d79da51..12f0891ce7f4 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -92,6 +92,7 @@ static struct rcu_state rcu_state =3D { > .exp_mutex =3D __MUTEX_INITIALIZER(rcu_state.exp_mutex), > .exp_wake_mutex =3D __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex), > .ofl_lock =3D __ARCH_SPIN_LOCK_UNLOCKED, > + .boot_exp_seq_poll_rq =3D RCU_GET_STATE_COMPLETED, > }; >=20 > /* Dump rcu_node combining tree at boot to verify correct setup. */ > @@ -4938,7 +4939,7 @@ void __init rcu_init(void) > qovld_calc =3D qovld; >=20 > // Kick-start any polled grace periods that started early. > - if (!(per_cpu_ptr(&rcu_data, cpu)->mynode->exp_seq_poll_rq & 0x1)) > + if (!(rcu_state.boot_exp_seq_poll_rq & 0x1)) > (void)start_poll_synchronize_rcu_expedited(); >=20 > rcu_test_sync_prims(); > diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h > index 192536916f9a..ae50ca6853ad 100644 > --- a/kernel/rcu/tree.h > +++ b/kernel/rcu/tree.h > @@ -397,6 +397,7 @@ struct rcu_state { > /* Synchronize offline with */ > /* GP pre-initialization. */ > int nocb_is_setup; /* nocb is setup from boot */ > + unsigned long boot_exp_seq_poll_rq; > }; >=20 > /* Values for rcu_state structure's gp_flags field. */ > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h > index 956cd459ba7f..1b35a1e233d9 100644 > --- a/kernel/rcu/tree_exp.h > +++ b/kernel/rcu/tree_exp.h > @@ -1068,9 +1068,11 @@ unsigned long start_poll_synchronize_rcu_expedited(= void) > if (rcu_init_invoked()) > raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags); > if (!poll_state_synchronize_rcu(s)) { > - rnp->exp_seq_poll_rq =3D s; > - if (rcu_init_invoked()) > + if (rcu_init_invoked()) { > + rnp->exp_seq_poll_rq =3D s; > queue_work(rcu_gp_wq, &rnp->exp_poll_wq); > + } else > + rcu_state.boot_exp_seq_poll_rq =3D s; > } > if (rcu_init_invoked()) > raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags); > --=20 > 2.25.1 >=20