linux-kernel - Re: [PATCH] mips/smp: Call rcu_cpu

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Date: Sat, 20 Jan 2024 07:38:14 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Stefan Wiehler <stefan.wiehler@...ia.com>
Cc: Florian Fainelli <f.fainelli@...il.com>, stable@...r.kernel.org,
	patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	linux@...ck-us.net, shuah@...nel.org, patches@...nelci.org,
	lkft-triage@...ts.linaro.org, pavel@...x.de, jonathanh@...dia.com,
	sudipm.mukherjee@...il.com, srw@...dewatkins.net, rwarsow@....de,
	conor@...nel.org, allen.lkml@...il.com,
	Huacai Chen <chenhuacai@...ngson.cn>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Subject: Re: [PATCH] mips/smp: Call rcu_cpu_starting() earlier

On Fri, Jan 19, 2024 at 05:38:11PM +0100, Stefan Wiehler wrote:
> rcu_cpu_starting() must be called before clockevents_register_device() to avoid
> the following lockdep splat triggered by calling list_add() when
> CONFIG_PROVE_RCU_LIST=y:
> 
>   WARNING: suspicious RCU usage
>   ...
>   -----------------------------
>   kernel/locking/lockdep.c:3680 RCU-list traversed in non-reader section!!
> 
>   other info that might help us debug this:
> 
>   RCU used illegally from offline CPU!
>   rcu_scheduler_active = 1, debug_locks = 1
>   no locks held by swapper/1/0.
>   ...
>   Call Trace:
>   [<ffffffff8012a434>] show_stack+0x64/0x158
>   [<ffffffff80a93d98>] dump_stack_lvl+0x90/0xc4
>   [<ffffffff801c9e9c>] __lock_acquire+0x1404/0x2940
>   [<ffffffff801cbf3c>] lock_acquire+0x14c/0x448
>   [<ffffffff80aa4260>] _raw_spin_lock_irqsave+0x50/0x88
>   [<ffffffff8021e0c8>] clockevents_register_device+0x60/0x1e8
>   [<ffffffff80130ff0>] r4k_clockevent_init+0x220/0x3a0
>   [<ffffffff801339d0>] start_secondary+0x50/0x3b8
> 
> raw_smp_processor_id() is required in order to avoid calling into lockdep
> before RCU has declared the CPU to be watched for readers.
> 
> See also commit 29368e093921 ("x86/smpboot:  Move rcu_cpu_starting() earlier"),
> commit de5d9dae150c ("s390/smp: move rcu_cpu_starting() earlier") and commit
> 99f070b62322 ("powerpc/smp: Call rcu_cpu_starting() earlier").
> 
> Signed-off-by: Stefan Wiehler <stefan.wiehler@...ia.com>
> Reviewed-by: Huacai Chen <chenhuacai@...ngson.cn>
> Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> ---
>  arch/mips/kernel/smp.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

What is the git commit id of this change in Linus's tree?  What
kernel(s) should this be applied to?

thanks,

greg k-h