linux-kernel - Re: [PATCH] ACPI / PPTT: get PPTT table in the first beginning

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Message-ID: <20210720133751.u6k6bdm7qco3gn65@bogus>
Date:   Tue, 20 Jul 2021 14:37:51 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc:     catalin.marinas@....com, will@...nel.org, rjw@...ysocki.net,
        viresh.kumar@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        guohanjun@...wei.com, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH] ACPI / PPTT: get PPTT table in the first beginning

On Tue, Jul 20, 2021 at 07:26:35PM +0800, Xiongfeng Wang wrote:
> When I added might_sleep() in down_timeout(), I got the following

Sorry it is not clear if you are able to reproduce this issue without
any other modifications in the mainline kernel ?

> Calltrace:
> 
> [    8.775671] BUG: sleeping function called from invalid context at kernel/locking/semaphore.c:160
> [    8.777070] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 14, name: cpuhp/0

>From this I guess you are adding sleep after raw_spin_lock_irqsave
in down_timeout(kernel/locking/semaphore.c).

> 
> It is because generic_exec_single() will disable local irq before
> calling _init_cache_level(). _init_cache_level() use acpi_get_table() to
> get the PPTT table, but this function could schedule out.
> 
> To fix this issue, we use a static pointer to record the mapped PPTT
> table in the first beginning. Later, we use that pointer to reference
> the PPTT table in acpi_find_last_cache_level(). We also modify other
> functions in pptt.c to use the pointer to reference PPTT table.
>

I don't follow this change at all.

-- 
Regards,
Sudeep