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Howlett" Cc: Andrew Morton , maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Geert Uytterhoeven , "Paul E. McKenney" , Christophe Leroy , Andreas Schwab , Matthew Wilcox , Peng Zhang , Ingo Molnar , Juri Lelli , Vincent Guittot , "Mike Rapoport (IBM)" , Vlastimil Babka Subject: Re: [PATCH] init/main: Clear boot task idle flag Message-ID: <20230913110139.GE692@noisy.programming.kicks-ass.net> References: <20230913005647.1534747-1-Liam.Howlett@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230913005647.1534747-1-Liam.Howlett@oracle.com> X-Rspamd-Queue-Id: E2E3B100011 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: zp1mfkb6or87wzk8ghu5fii5s9ngrejp X-HE-Tag: 1694602914-160394 X-HE-Meta: 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 fo6SnG1K 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 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 Tue, Sep 12, 2023 at 08:56:47PM -0400, Liam R. Howlett wrote: > Initial booting is setting the task flag to idle (PF_IDLE) by the call > path sched_init() -> init_idle(). Having the task idle and calling > call_rcu() in kernel/rcu/tiny.c means that TIF_NEED_RESCHED will be > set. Subsequent calls to any cond_resched() will enable IRQs, > potentially earlier than the IRQ setup has completed. Recent changes > have caused just this scenario and IRQs have been enabled early. > > This causes a warning later in start_kernel() as interrupts are enabled > before they are fully set up. > > Fix this issue by clearing the PF_IDLE flag on return from sched_init() > and restore the flag in rest_init(). Although the boot task was marked > as idle since (at least) d80e4fda576d, I am not sure that it is wrong to > do so. The forced context-switch on idle task was introduced in the > tiny_rcu update, so I'm going to claim this fixes 5f6130fa52ee. > > Link: https://lore.kernel.org/linux-mm/87v8cv22jh.fsf@mail.lhotse/ > Link: https://lore.kernel.org/linux-mm/CAMuHMdWpvpWoDa=Ox-do92czYRvkok6_x6pYUH+ZouMcJbXy+Q@mail.gmail.com/ > Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task") > Cc: stable@vger.kernel.org > Cc: Geert Uytterhoeven > Cc: "Paul E. McKenney" > Cc: Christophe Leroy > Cc: Andreas Schwab > Cc: Matthew Wilcox > Cc: Peng Zhang > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Juri Lelli > Cc: Vincent Guittot > Cc: Andrew Morton > Cc: "Mike Rapoport (IBM)" > Cc: Vlastimil Babka > Signed-off-by: Liam R. Howlett > --- > init/main.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/init/main.c b/init/main.c > index ad920fac325c..f74772acf612 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -696,7 +696,7 @@ noinline void __ref __noreturn rest_init(void) > */ > rcu_read_lock(); > tsk = find_task_by_pid_ns(pid, &init_pid_ns); > - tsk->flags |= PF_NO_SETAFFINITY; > + tsk->flags |= PF_NO_SETAFFINITY | PF_IDLE; > set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id())); > rcu_read_unlock(); > > @@ -938,6 +938,8 @@ void start_kernel(void) > * time - but meanwhile we still have a functioning scheduler. > */ > sched_init(); > + /* Avoid early context switch, rest_init() restores PF_IDLE */ > + current->flags &= ~PF_IDLE; > > if (WARN(!irqs_disabled(), > "Interrupts were enabled *very* early, fixing it\n")) Hurmph... so since this is about IRQs, would it not make sense to have the | PF_IDLE near 'early_boot_irqs_disabled = false' ? Or, alternatively, make the tinyrcu thing check that variable?