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Date:   Tue, 12 Sep 2023 15:09:29 -0400
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Andreas Schwab <schwab@linux-m68k.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        maple-tree@lists.infradead.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        linuxppc-dev@lists.ozlabs.org,
        Michael Ellerman <mpe@ellerman.id.au>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: [PATCH v2 1/2] maple_tree: Disable mas_wr_append() when other
 readers are possible
Message-ID: <20230912190929.54kxm7wyws7pgcsv@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Andreas Schwab <schwab@linux-m68k.org>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        maple-tree@lists.infradead.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        linuxppc-dev@lists.ozlabs.org,
        Michael Ellerman <mpe@ellerman.id.au>,
        Geert Uytterhoeven <geert@linux-m68k.org>
References: <20230819004356.1454718-1-Liam.Howlett@oracle.com>
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* Andreas Schwab <schwab@linux-m68k.org> [230912 14:15]:
> Any news?  This is still broken.

I have a proposed fix.  I seem to have caused a pre-existing problem to
show up.  Please see if the attached works for you, and I'll send it
to a lot of people.

Thanks,
Liam

--5aqidbzt6oq7a3jx
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	filename="0001-init-main-Clear-boot-task-idle-flag.patch"
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From 9ef8f834bb0342dc26464b9dd0165929d3e6a7e5 Mon Sep 17 00:00:00 2001
From: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Date: Tue, 12 Sep 2023 13:45:29 -0400
Subject: [PATCH] init/main: Clear boot task idle flag

Initial booting was 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
enabled.  Subsequent calls to any cond_resched() will enable IRQs,
potentially earlier than the enabling of IRQs.

This causes a warning later in start_kernel() as interrupts are enabled
before the 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().

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 init/main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/init/main.c b/init/main.c
index ad920fac325c..46b35be8f00a 100644
--- a/init/main.c
+++ b/init/main.c
@@ -696,7 +696,7 @@ noinline void __ref __noreturn rest_init(void)
 	 */
 	rcu_read_lock();
 	tsk =3D find_task_by_pid_ns(pid, &init_pid_ns);
-	tsk->flags |=3D PF_NO_SETAFFINITY;
+	tsk->flags |=3D PF_NO_SETAFFINITY | PF_IDLE;
 	set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id()));
 	rcu_read_unlock();
=20
@@ -938,6 +938,7 @@ void start_kernel(void)
 	 * time - but meanwhile we still have a functioning scheduler.
 	 */
 	sched_init();
+	current->flags &=3D ~PF_IDLE;
=20
 	if (WARN(!irqs_disabled(),
 		 "Interrupts were enabled *very* early, fixing it\n"))
--=20
2.39.2


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