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McKenney" Cc: Sebastian Andrzej Siewior , frederic@kernel.org, neeraj.iitr10@gmail.com, urezki@gmail.com, joelagnelf@nvidia.com, boqun.feng@gmail.com, rcu@vger.kernel.org, Kumar Kartikeya Dwivedi Subject: Re: Next-level bug in SRCU implementation of RCU Tasks Trace + PREEMPT_RT Message-ID: References: <20260318105058.j2aKncBU@linutronix.de> <20260318144305.xI6RDtzk@linutronix.de> <76ef9a5e-7343-4b8e-bf3c-cabd8753ecdb@paulmck-laptop> <20260318160445.IyUiWV0T@linutronix.de> <06a0cb91-1737-4691-a810-8340e1acf1d6@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <06a0cb91-1737-4691-a810-8340e1acf1d6@paulmck-laptop> On Wed, Mar 18, 2026 at 09:32:07AM -0700, Paul E. McKenney wrote: > On Wed, Mar 18, 2026 at 05:04:45PM +0100, Sebastian Andrzej Siewior wrote: > > On 2026-03-18 08:43:32 [-0700], Paul E. McKenney wrote: > > > > Your patch just s/spinlock_t/raw_spinlock_t so we get the locking/ > > > > nesting right. The wakeup problem remains, right? > > > > But looking at the code, there is just srcu_funnel_gp_start(). If its > > > > srcu_schedule_cbs_sdp() / queue_delayed_work() usage is always delayed > > > > then there will be always a timer and never a direct wake up of the > > > > worker. Wouldn't that work? > > > > > > Right, that patch fixes one lockdep problem, but another remains. > > > > What remains? > > With that patch, we no longer have call_srcu() directly acquiring a > non-raw spinlock, but as you say, we still have the wakeup problem. > I don't think we have a wakeup problem since we use workqueue to defer the wakeup, but maybe I'm missing something here? Regards, Boqun