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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 v2] kernel/sched: Modify initial boot task idle setup Message-ID: <20230919084924.GB21729@noisy.programming.kicks-ass.net> References: <20230915174444.2835306-1-Liam.Howlett@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230915174444.2835306-1-Liam.Howlett@oracle.com> X-Stat-Signature: 784rsakcrib7osg4meujussfoq5x3ghj X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E7FE81C001B X-Rspam-User: X-HE-Tag: 1695113507-355108 X-HE-Meta: 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 ZkDGmxWR K6jQrWQyjvF3oeEFaoemzsgKsb/HY7gdbt3ttmCYfGEe7q2S/Mgz+Cw4Ab3tUF7MCHUwaOE78HvprLAJR8gVTZeCIlGYCG29SGadXXrRMVG8G/TInvMOZKxwxgIRn74jDhOeA6ai4nLPYbBuKYIwSpeDkw70mvdUCqjClqm9sc1n3Sh58RvnwJeVq4CP7wVFz5FjDd22nZYCkNyJrkxoXdQ6BJKJ1IYfR58jyI1EGRZI+dlKq8Z1imcBw/g== 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 Fri, Sep 15, 2023 at 01:44:44PM -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 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=Ox-do92czYRvkok6_x6pYUH+ZouMcJbXy+Q@mail.gmail.com/ > Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task") > Signed-off-by: Liam R. Howlett > --- Thanks!, I've queued this up for sched/urgent but will let the robots at it before I push it out to -tip.