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[209.85.128.169]) by smtp.gmail.com with ESMTPSA id b2-20020a0df202000000b005950e1bbf11sm3076493ywf.60.2023.09.19.03.11.33 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Sep 2023 03:11:33 -0700 (PDT) Received: by mail-yw1-f169.google.com with SMTP id 00721157ae682-59bc97d7b3dso84188617b3.1 for ; Tue, 19 Sep 2023 03:11:33 -0700 (PDT) X-Received: by 2002:a81:a04b:0:b0:577:3cd0:3728 with SMTP id x72-20020a81a04b000000b005773cd03728mr2309678ywg.14.1695118293278; Tue, 19 Sep 2023 03:11:33 -0700 (PDT) MIME-Version: 1.0 References: <20230915174444.2835306-1-Liam.Howlett@oracle.com> In-Reply-To: <20230915174444.2835306-1-Liam.Howlett@oracle.com> From: Geert Uytterhoeven Date: Tue, 19 Sep 2023 12:11:22 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2] kernel/sched: Modify initial boot task idle setup To: "Liam R. Howlett" Cc: Andrew Morton , maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, "Paul E. McKenney" , Christophe Leroy , Andreas Schwab , Matthew Wilcox , Peng Zhang , Peter Zijlstra , Ingo Molnar , Juri Lelli , Vincent Guittot , "Mike Rapoport (IBM)" , Vlastimil Babka , Linux-Renesas Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: A4C2940028 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: zrw5naj6pxdcgkg3ipw1f8rhtudyru4q X-HE-Tag: 1695118295-391221 X-HE-Meta: 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 CS9XPBPD 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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: Hi Liam, On Fri, Sep 15, 2023 at 7:45=E2=80=AFPM 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 setting the PF_IDLE flag later in the boot sequence. > > 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=3DOx-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 Thanks for your patch! This fixes the WARNING: CPU: 0 PID: 0 at init/main.c:992 start_kernel+0x2f0/0x480 I was seeing during boot on Renesas RZ/A1 and RZ/A2 since commit cfeb6ae8bcb96ccf ("maple_tree: disable mas_wr_append() when other readers are possible") in v6.5. And unlike v1, this does not cause lots of new warnings on e.g. R-Car M2-W. Tested-by: Geert Uytterhoeven Gr{oetje,eeting}s, Geert --=20 Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k= .org In personal conversations with technical people, I call myself a hacker. Bu= t when I'm talking to journalists I just say "programmer" or something like t= hat. -- Linus Torvalds