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

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Date: Sun, 21 Jan 2024 08:52:55 -0800
From: Florian Fainelli <f.fainelli@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Stefan Wiehler <stefan.wiehler@...ia.com>
Cc: 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 1/19/2024 10:38 PM, Greg Kroah-Hartman wrote:
> 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?

The upstream commit is 55702ec9603ebeffb15e6f7b113623fe1d8872f4 
("mips/smp: Call rcutree_report_cpu_starting() earlier") and this change 
from Stefan should be applied to both the 6.1 stable and 6.6 stable 
branches. Thanks!
-- 
Florian