linux-kernel - Re: [PATCH] ACPI: only free map once in osl.c

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Date:   Thu, 21 Nov 2019 22:57:20 +0000
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Francesco Ruggeri <fruggeri@...sta.com>
Cc:     lenb@...nel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        open list <linux-kernel@...r.kernel.org>,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH] ACPI: only free map once in osl.c

On 11/21/19 10:49 PM, Francesco Ruggeri wrote:
> On Thu, Nov 21, 2019 at 1:19 PM Dmitry Safonov <0x7f454c46@...il.com> wrote:
>>
>> Hi Francesco,
>>
>> I believe, there's still an issue with your patch.
>>
>> On Wed, 20 Nov 2019 at 05:50, Francesco Ruggeri <fruggeri@...sta.com> wrote:
>>> @@ -472,10 +477,11 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
>>>                 mutex_unlock(&acpi_ioremap_lock);
>>>                 return;
>>>         }
>>> -       acpi_os_drop_map_ref(map);
>>> +       refcount = acpi_os_drop_map_ref(map);
>>>         mutex_unlock(&acpi_ioremap_lock);
>>
>> Here comes acpi_os_get_iomem() increasing the refcount again.
> 
> Thanks Dmitry.
> I think that any code that increments the refcount does so after
> looking for map in acpi_ioremap under acpi_ioremap_lock,
> and the process that drops the last reference removes map
> from the list, also under acpi_ioremap_lock, so I am not sure
> this could happen.
> The synchronize_rcu_expedited in acpi_os_map_cleanup should
> then take care of any other references to map (which it is my
> understanding require acpi_ioremap_lock or rcu read lock).

Ah, right you are!
Sorry for a false alarm.

Thanks,
          Dmitry