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McKenney" Cc: Boqun Feng , Qian Cai , Steven Rostedt , Ingo Molnar , x86 , linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Linux Next Mailing List , Stephen Rothwell Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion Message-ID: <20201015095235.GT2651@hirez.programming.kicks-ass.net> References: <20201013112544.GZ2628@hirez.programming.kicks-ass.net> <20201013162650.GN3249@paulmck-ThinkPad-P72> <20201013193025.GA2424@paulmck-ThinkPad-P72> <20201014183405.GA27666@paulmck-ThinkPad-P72> <20201014215319.GF2974@worktop.programming.kicks-ass.net> <20201014221152.GS3249@paulmck-ThinkPad-P72> <20201014223954.GH2594@hirez.programming.kicks-ass.net> <20201014235553.GU3249@paulmck-ThinkPad-P72> <20201015034128.GA10260@paulmck-ThinkPad-P72> <20201015094926.GY2611@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201015094926.GY2611@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 15, 2020 at 11:49:26AM +0200, Peter Zijlstra wrote: > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1764,8 +1764,7 @@ static bool rcu_gp_init(void) > smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values. > firstseq = READ_ONCE(rnp->ofl_seq); > if (firstseq & 0x1) > - while (firstseq == smp_load_acquire(&rnp->ofl_seq)) > - schedule_timeout_idle(1); // Can't wake unless RCU is watching. > + smp_cond_load_relaxed(&rnp->ofl_seq, VAL == firstseq); My bad, that should be: VAL != firstseq. > smp_mb(); // Pair with barriers used when updating ->ofl_seq to even values. > raw_spin_lock(&rcu_state.ofl_lock); > raw_spin_lock_irq_rcu_node(rnp);