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From: "Zqiang" Message-ID: <1133458227af4b9a7a0cee284502a0643f1fad3f@linux.dev> TLS-Required: No Subject: Re: [PATCH v2] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if_needed() To: paulmck@kernel.org Cc: "Joel Fernandes" , frederic@kernel.org, neeraj.upadhyay@kernel.org, boqun.feng@gmail.com, urezki@gmail.com, rcu@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <430d5714-4a00-4a75-b763-34918f8017c3@paulmck-laptop> References: <20250909133928.615218-1-qiang.zhang@linux.dev> <4c7d977b-7d09-48e0-9a88-bae93fa5e401@paulmck-laptop> <20250910143620.GA561834@joelbox2> <70fa9fd07e4fe2b1b498109f3450804e731fd7ce@linux.dev> <430d5714-4a00-4a75-b763-34918f8017c3@paulmck-laptop> X-Migadu-Flow: FLOW_OUT >=20 >=20On Thu, Sep 11, 2025 at 12:36:45AM +0000, Zqiang wrote: >=20 >=20>=20 >=20> On Wed, Sep 10, 2025 at 10:36:20AM -0400, Joel Fernandes wrote: > >=20=20 >=20> >=20 >=20> > [..] > > > > kernel/rcu/srcutiny.c | 4 +--- > > > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > >=20 >=20> > > diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c > > > > index b52ec45698e8..b2da188133fc 100644 > > > > --- a/kernel/rcu/srcutiny.c > > > > +++ b/kernel/rcu/srcutiny.c > > > > @@ -181,10 +181,9 @@ static void srcu_gp_start_if_needed(struct = srcu_struct *ssp) > > > > { > > > > unsigned long cookie; > > > >=20 >=20> > > - preempt_disable(); // Needed for PREEMPT_LAZY > > > > + lockdep_assert_preemption_disabled(); > > >=20 >=20> > nit: Do we still want to keep the comment that the expectation o= f preemption > > > being disabled is for the LAZY case? > > >=20 >=20> Good point, and I do believe that we do. Zqiang, any reason not to > > add this comment back in? > >=20=20 >=20> in rcu-tree, this commit: > >=20=20 >=20> (935147775c977 "EXP srcu: Enable Tiny SRCU On all CONFIG_SMP=3Dn k= ernels") > >=20=20 >=20> make preempt disable needed for CONFIG_PREEMPT=3Dy or CONFIG_PREEM= PT_LAZY=3Dy > > when the CONFIG_SMP=3Dn. do we need to replace "Needed for PREEMPT_L= AZY" > > comments with "Needed for PREEMPT or PREEMPT_LAZY"? > >=20 >=20Good point as well, thank you! And I need to decide whether I should > send that patch upstream. Its original purpose was to test PREEMPT_LAZY= =3Dy > better than could be tested with PREEMPT_LAZY. >=20 >=20Thoughts? I will add "Needed for PREEMPT_LAZY" comments, if this commit (935147775c= 977) is send to upstream, will update comments again in the future. Thanks Zqiang >=20 >=20 Thanx, Paul >=20 >=20>=20 >=20> Thanks > > Zqiang > >=20=20 >=20>=20=20 >=20>=20=20 >=20> Thanx, Paul > >=20=20 >=20> >=20 >=20> > thanks, > > >=20 >=20> > - Joel > > >=20 >=20> >=20 >=20> > > cookie =3D get_state_synchronize_srcu(ssp); > > > > if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) { > > > > - preempt_enable(); > > > > return; > > > > } > > > > WRITE_ONCE(ssp->srcu_idx_max, cookie); > > > > @@ -194,7 +193,6 @@ static void srcu_gp_start_if_needed(struct s= rcu_struct *ssp) > > > > else if (list_empty(&ssp->srcu_work.entry)) > > > > list_add(&ssp->srcu_work.entry, &srcu_boot_list); > > > > } > > > > - preempt_enable(); > > > > } > > > >=20 >=20> > > /* > > > > --=20 >=20> > > 2.48.1 > > > > > > > > > >