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SubjectRe: [PATCH 3/4] [Patch-next] ACPI, APEI Fix the return value(==NULL) of acpi_pre_map always.
(2010/08/17 10:37), Huang Ying wrote:
> On Tue, 2010-08-17 at 08:56 +0800, Jin Dongming wrote:
>> acpi_pre_map() is used for remapping the physical address of I/O, so
>> it should be return NULL or remapped virtual address. The problem
>> is whether I/O remapping is successful or not, the function returns
>> NULL always.
>
> No. NULL is returned for error path only. Please check the code again.

There three places used the local variable vaddr in acpi_pre_map() in next-tree.
1. 115 vaddr = __acpi_try_ioremap(paddr, size);
2. 122 vaddr = ioremap(pg_off, pg_sz);
3. 135 vaddr = __acpi_try_ioremap(paddr, size);

Let's think about the following statement.
Assumption: the physical address has never been remapped.
Step:
1. vaddr == NULL
Because the physical address is not registered in the acpi_iomaps,
it should be returned NULL from __acpi_try_ioremap().

2. vaddr == the virtual address of the physical address.
Here if ioremap is successful, the value of vaddr should be
the virtual address returned from ioremap().

3. vaddr == NULL <== IMPORTANT
Here it is because the physical address has not been registered
in the acpi_iomaps yet, it still return NULL from __acpi_try_ioremap().
So it is why vaddr == NULL, even if the physical address has never
been remapped.

Result: vaddr == NULL.

And if the vaddr is not NULL, it could not be added into acpi_iomaps.
Codes in acpi_pre_map() is like following.

134 spin_lock_irqsave(&acpi_iomaps_lock, flags);
135 vaddr = __acpi_try_ioremap(paddr, size); <== the 3rd step
136 if (vaddr) {
137 spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
138 iounmap(map->vaddr);
139 kfree(map);
140 return vaddr;
141 }
142 list_add_tail_rcu(&map->list, &acpi_iomaps); <== add into acpi_iomaps.
143 spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
>
>> In acpi_pre_map(), after the physical address is remapped sucessfully,
>> it will check whether the physical address has been added into acpi_iomaps
>> list again. If the physical address has beed added into acpi_iomaps,
>> the virtual address will be saved in vaddr. Otherwise, NULL be saved in
>> vaddr.
>>
>> So if the physical address has never been remapped, the return value of
>> acpi_pre_map will be NULL always.
>>
>> This patch fixed it and I confirmed it on x86_64 next-tree.
>>
>> Signed-off-by: Jin Dongming <jin.dongming@np.css.fujitsu.com>
>> ---
>> drivers/acpi/atomicio.c | 4 ++--
>> 1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/acpi/atomicio.c b/drivers/acpi/atomicio.c
>> index 8f8bd73..1bc2614 100644
>> --- a/drivers/acpi/atomicio.c
>> +++ b/drivers/acpi/atomicio.c
>> @@ -133,7 +133,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
>>
>> spin_lock_irqsave(&acpi_iomaps_lock, flags);
>> vaddr = __acpi_try_ioremap(paddr, size);
>> - if (vaddr) {
>> + if (unlikely(vaddr)) {
>
> pre_map is not performance critical, so "unlikely" here helps little.
>
>> spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
>> iounmap(map->vaddr);
>> kfree(map);
>> @@ -142,7 +142,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
>> list_add_tail_rcu(&map->list, &acpi_iomaps);
>> spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
>>
>> - return vaddr + (paddr - pg_off);
>> + return map->vaddr + (paddr - pg_off);
>> err_unmap:
>> iounmap(vaddr);
>> return NULL;
>
> When will vaddr != map->vaddr?
>
> Best Regards,
> Huang Ying
>
>
>
>




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