Hi, Bjorn Helgaas
I will modify this patch and resend it as soon as possible in next week.
Best Regards,
Jin Dongming
(2010/09/03 0:47), Bjorn Helgaas wrote:
> On Thursday, September 02, 2010 01:20:18 am 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
>> that when (paddr - pg_off) equals 0, no matter whether I/O remapping is
>> successful or not, the function returns NULL.
>>
>> In acpi_pre_map(), after the physical address is remapped successfully,
>> it will check whether the physical address has been added into acpi_iomaps
>> list again.
>> - If the physical address has been added into acpi_iomaps, the virtual
>> address will be saved in vaddr.
>> - Otherwise, NULL be saved in vaddr.
>>
>> So if the physical address is the first time to be remapped, vaddr will be
>> NULL always.
>>
>> In many cases, (paddr - pg_off) may not equal 0. So the function could work
>> well. In our machine, (paddr - pg_off) equals 0, so the return value of
>> acpi_pre_map() is NULL.
>>
>> This patch fixed it and I confirmed it on x86_64 next-tree.
>
> This description is complicated and obscures the very simple bug
> you are fixing. I suggest something like this:
>
> ACPI: fix acpi_pre_map() return value
>
> After we ioremap() a new region, we call __acpi_try_ioremap() to
> see whether another thread has already mapped the same region.
> This check clobbers "vaddr", so compute the return value using
> the ioremap() result "map->vaddr" instead.
>
>> v2:
>> Modified the unsuitable description of patch.
>>
>> v3:
>> Modified the wrong words in the description of patch.
>>
>> Signed-off-by: Jin Dongming <jin.dongming@xxxxxxxxxxxxxxxxxx>
>> Acked-by: Huang Ying <ying.huang@xxxxxxxxx>
>> ---
>> 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)) {
>
> This "unlikely" addition also obscures things. It's completely
> unrelated to the bug you're fixing, so it should be in a different
> patch, and I'm dubious that there's enough performance advantage to
> compensate for the decreased code readability. I wouldn't make this
> change unless you can measure a performance improvement.
>
>> 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);
>
> Since you're changing this line anyway, I think you should change it to:
>
> return map->vaddr + (paddr - map->paddr);
>
> so it matches __acpi_try_ioremap().
>
>> err_unmap:
>> iounmap(vaddr);
>> return NULL;
>> -- 1.7.1.
>>
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