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From: Xiongfeng Wang <>
To: Sudeep Holla <>
Cc: <>, <>, <>,
	<>, <>,
	<>, <>,
Subject: Re: [PATCH] ACPI / PPTT: get PPTT table in the first beginning
Date: Wed, 21 Jul 2021 09:25:23 +0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210720133751.u6k6bdm7qco3gn65@bogus>

Hi Sudeep,

On 2021/7/20 21:37, Sudeep Holla wrote:
> 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 ?

Without any modifications, the mainline kernel does not print the Calltrace. But
the risk of sleeping in atomic context still exists.

>> 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).

I add 'might_sleep()' which is used to check whether there are problems if I
sleep here. It's not a real sleep.

The Document for might_sleep is as below.
 * might_sleep - annotation for functions that can sleep

 * this macro will print a stack trace if it is executed in an atomic
 * context (spinlock, irq-handler, ...). Additional sections where blocking is
 * not allowed can be annotated with non_block_start() and non_block_end()
 * pairs.
 * This is a useful debugging help to be able to catch problems early and not
 * be bitten later when the calling function happens to sleep when it is not
 * supposed to.

>> 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.

The main problem is that we called local_irq_save() in generic_exec_single(),
and then we called down_timeout() in acpi_os_wait_semaphore(). down_timeout()
could enter into sleep if failed to acquire the semaphore. There are risks of
sleeping in irq disabled context.


> I don't follow this change at all.

  reply	other threads:[~2021-07-21  1:25 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-20 11:26 Xiongfeng Wang
2021-07-20 13:37 ` Sudeep Holla
2021-07-21  1:25   ` Xiongfeng Wang [this message]
2021-09-01  7:29   ` Zenghui Yu
2021-09-01  8:15     ` Hanjun Guo
2021-09-01  8:49       ` Zenghui Yu

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