Re: [PATCH v3] firmware: arm_sdei: Fix sleep from invalid context BUG

[James Morse]

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 It got superseded by pNMI and this early slot is not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@xxxxxxx>


Will, are you happy to pick this up and fix the typos, or would you prefer a clean version
to be posted?


Thanks,

James