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Message-ID: <CAHk-=wg+jqA6nt36TxAfoqWskRAzhVfzBejcK6PNYXC+QcwyiA@mail.gmail.com>
Date: Mon, 3 Jul 2023 10:07:28 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Conor Dooley <conor@...nel.org>,
Anup Patel <apatel@...tanamicro.com>,
Palmer Dabbelt <palmer@...osinc.com>,
Marc Zyngier <maz@...nel.org>
Cc: lkp <oliver.sang@...el.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
lkp@...el.com
Subject: Re: [mm] 408579cd62: WARNING:suspicious_RCU_usage
On Mon, 3 Jul 2023 at 10:00, Conor Dooley <conor@...nel.org> wrote:
>
> I'm not entirely sure if it is related, as stuff in the guts of mm like
> this is beyond me, but I've been seeing similar warnings on RISC-V.
No, that RISC-V warning is also about bad RCU usage, but that's a
different thing.
> RCU used illegally from offline CPU!
> rcu_scheduler_active = 1, debug_locks = 1
> 1 lock held by swapper/1/0:
> #0: ffffffff8169ceb0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x32
>
> stack backtrace:
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.4.0-10173-ga901a3568fd2 #1
> Hardware name: riscv-virtio,qemu (DT)
> Call Trace:
> [<ffffffff80006a20>] show_stack+0x2c/0x38
> [<ffffffff80af3ee0>] dump_stack_lvl+0x5e/0x80
> [<ffffffff80af3f16>] dump_stack+0x14/0x1c
> [<ffffffff80083ff0>] lockdep_rcu_suspicious+0x19e/0x232
> [<ffffffff80ad4802>] mtree_load+0x18a/0x3b6
> [<ffffffff80091632>] __irq_get_desc_lock+0x2c/0x82
> [<ffffffff80094722>] enable_percpu_irq+0x36/0x9e
> [<ffffffff800087d4>] riscv_ipi_enable+0x32/0x4e
> [<ffffffff80008692>] smp_callin+0x24/0x66
This is also triggering on the maple tree sanity checks, but it' sa
different maple tree, and a different code sequence.
And a different case of suspicious RCU usage - not a lack of locking,
but simply using RCU before marking the CPU online.
I suspect the riscv_ipi_enable() in the RISC-V version of smp_callin()
needs to be moved down to below the
set_cpu_online(curr_cpuid, 1);
or was there some reason why it needed to be done quite _that_ early
in commit 832f15f42646 ("RISC-V: Treat IPIs as normal Linux IRQs")?
Added guilty parties to the cc.
Linus
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