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[209.85.219.175]) by smtp.gmail.com with ESMTPSA id b65-20020a0df244000000b005869fd2b5bcsm3119414ywf.127.2023.09.13.05.58.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Sep 2023 05:58:32 -0700 (PDT) Received: by mail-yb1-f175.google.com with SMTP id 3f1490d57ef6-d8164e661abso447866276.1; Wed, 13 Sep 2023 05:58:32 -0700 (PDT) X-Received: by 2002:a25:c7cb:0:b0:d7f:8e1f:6df0 with SMTP id w194-20020a25c7cb000000b00d7f8e1f6df0mr2208489ybe.2.1694609912250; Wed, 13 Sep 2023 05:58:32 -0700 (PDT) MIME-Version: 1.0 References: <20230913005647.1534747-1-Liam.Howlett@oracle.com> In-Reply-To: <20230913005647.1534747-1-Liam.Howlett@oracle.com> From: Geert Uytterhoeven Date: Wed, 13 Sep 2023 14:58:20 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] init/main: Clear boot task idle flag 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: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Liam, On Wed, Sep 13, 2023 at 2:57 AM 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 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. However, this causes lots of new warnings on e.g. R-Car M2-W, which wasn't affected before, like: +BUG: sleeping function called from invalid context at kernel/sched/completion.c:111 +in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper/0 +preempt_count: 0, expected: 0 +no locks held by swapper/0/1. +CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 6.6.0-rc1-koelsch-02359-g9a5bed6a8bd8 #1864 +Hardware name: Generic R-Car Gen2 (Flattened Device Tree) + unwind_backtrace from show_stack+0x10/0x14 + show_stack from dump_stack_lvl+0x68/0x90 + dump_stack_lvl from __might_resched+0x1b0/0x22c + __might_resched from __wait_for_common+0x38/0x170 + __wait_for_common from kernel_init+0x10/0x130 + kernel_init from ret_from_fork+0x14/0x30 +Exception stack(0xf0815fb0 to 0xf0815ff8) +5fa0: 00000000 00000000 00000000 00000000 +5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 +5fe0: 00000000 00000000 00000000 00000000 00000013 00000000 and +BUG: sleeping function called from invalid context at kernel/locking/mutex.c:580 +in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd +preempt_count: 0, expected: 0 +no locks held by systemd/1. +CPU: 1 PID: 1 Comm: systemd Tainted: G W N 6.6.0-rc1-koelsch-02359-g9a5bed6a8bd8 #1864 +Hardware name: Generic R-Car Gen2 (Flattened Device Tree) + unwind_backtrace from show_stack+0x10/0x14 + show_stack from dump_stack_lvl+0x68/0x90 + dump_stack_lvl from __might_resched+0x1b0/0x22c + __might_resched from __mutex_lock+0x34/0x3a8 + __mutex_lock from mutex_lock_nested+0x18/0x20 + mutex_lock_nested from do_epoll_wait+0x220/0x5ac + do_epoll_wait from sys_epoll_wait+0x44/0x6c + sys_epoll_wait from ret_fast_syscall+0x0/0x1c +Exception stack(0xf0815fa8 to 0xf0815ff0) +5fa0: beff75e0 00000004 00000004 beff75e0 0000003b ffffffff +5fc0: beff75e0 00000004 ffffffff 000000fc 00000000 ffffffff 0000003b 00000004 +5fe0: 000000fc beff75b8 b6ef8511 b6e75786 Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds