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Message-ID: <6c0fd4d4-9424-172f-e17e-66c0267abd92@arm.com>
Date:   Thu, 16 Feb 2023 09:51:42 +0100
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Subject: Re: [PATCH v3] firmware: arm_sdei: Fix sleep from invalid context BUG
To:     James Morse <james.morse@arm.com>, Will Deacon <will@kernel.org>
Cc:     Huacai Chen <chenhuacai@kernel.org>,
        Atish Patra <atishp@atishpatra.org>,
        Shaokun Zhang <zhangshaokun@hisilicon.com>,
        WANG Xuerui <git@xen0n.name>,
        Guangbin Huang <huangguangbin2@huawei.com>,
        Bharat Bhushan <bbhushan2@marvell.com>,
        Bibo Mao <maobibo@loongson.cn>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Juergen Gross <jgross@suse.com>,
        Nick Child <nnac123@linux.ibm.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20230215160949.94602-1-pierre.gondois@arm.com>
 <2b06fd6c-83d5-3dbe-0227-02091f5d3dac@arm.com>
Content-Language: en-US
From:   Pierre Gondois <pierre.gondois@arm.com>
In-Reply-To: <2b06fd6c-83d5-3dbe-0227-02091f5d3dac@arm.com>
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On 2/15/23 19:13, James Morse wrote:
> Hi Pierre, Will,
> 
> On 15/02/2023 16:09, Pierre Gondois wrote:
>> Running a preemp_rt kernel based on vv6.2-rc3-rt1 based kernel on an
>> Ampere Altra triggers:
>>    BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
>>    in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 24, name: cpuhp/0
>>    preempt_count: 0, expected: 0
>>    RCU nest depth: 0, expected: 0
>>    3 locks held by cpuhp/0/24:
>>     #0: ffffda30217c70d0 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
>>     #1: ffffda30217c7120 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
>>     #2: ffffda3021c711f0 (sdei_list_lock){....}-{3:3}, at: sdei_cpuhp_up+0x3c/0x130
>>    irq event stamp: 36
>>    hardirqs last  enabled at (35): [<ffffda301e85b7bc>] finish_task_switch+0xb4/0x2b0
>>    hardirqs last disabled at (36): [<ffffda301e812fec>] cpuhp_thread_fun+0x21c/0x248
>>    softirqs last  enabled at (0): [<ffffda301e80b184>] copy_process+0x63c/0x1ac0
>>    softirqs last disabled at (0): [<0000000000000000>] 0x0
>>    CPU: 0 PID: 24 Comm: cpuhp/0 Not tainted 5.19.0-rc3-rt5-[...]
>>    Hardware name: WIWYNN Mt.Jade Server [...]
>>    Call trace:
>>     dump_backtrace+0x114/0x120
>>     show_stack+0x20/0x70
>>     dump_stack_lvl+0x9c/0xd8
>>     dump_stack+0x18/0x34
>>     __might_resched+0x188/0x228
>>     rt_spin_lock+0x70/0x120
>>     sdei_cpuhp_up+0x3c/0x130
>>     cpuhp_invoke_callback+0x250/0xf08
>>     cpuhp_thread_fun+0x120/0x248
>>     smpboot_thread_fn+0x280/0x320
>>     kthread+0x130/0x140
>>     ret_from_fork+0x10/0x20
>>
>> sdei_cpuhp_up() is called in the STARTING hotplug section,
>> which runs whith interrupts disabled. Use a CPUHP_AP_ONLINE_DYN entry
> 
> Typo: with
> 
>> instead to execute the cpuhp cb later, with preemption enabled.
>>
>> SDEI originaly got its own cpuhp slot because to allow interracting
> 
> Typo: originally
> Typo: interacting
> 
>> with perf. It got superseded by pNMI and this early slot is not
>> relevant anymore. [1]
> 
> (Please add a spell checker to your workflow. 'codespell' knows which bits of
>   a diff it should check)
> 
> "because to allow interacting" isn't easy to parse, "to allow an interaction with"?
> 
> 
>> Some SDEI calls (e.g. SDEI_1_0_FN_SDEI_PE_MASK) take actions on the
>> calling CPU. It is checked that preemption is disabled for them.
>> _ONLINE cpuhp cb are executed in the 'per CPU hotplug thread'.
>> Preemption is enabled in those threads, but their cpumask is limited
>> to 1 CPU.
>> Move 'WARN_ON_ONCE(preemptible())' statements so that SDEI cpuhp cb
>> don't trigger them.
>>
>> Also add a check for the SDEI_1_0_FN_SDEI_PRIVATE_RESET SDEI call
>> which acts on the calling CPU.
> 
> Thanks for sticking with this,
> 
> Reviewed-by: James Morse <james.morse@arm.com>
> 
> 
> Will, are you happy to pick this up and fix the typos, or would you prefer a clean version
> to be posted?

I re-posted the patch with the typos corrected at:
https://lore.kernel.org/all/20230216084920.144064-1-pierre.gondois@arm.com/

sorry for those,
Regards,
Pierre

> 
> 
> Thanks,
> 
> James