linux-kernel - Re: [PATCH 6 of 7] x86: use early_ioremap in __acpi_map

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Date:	Thu, 11 Sep 2008 13:34:12 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 6 of 7] x86: use early_ioremap in __acpi_map_table

On Wed, Sep 10, 2008 at 9:49 AM, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> Ingo Molnar wrote:
>>> So i'd suggest a different, more carful approach: keep the new code
>>> you wrote, but print a WARN()ing if prev_map is not unmapped yet when
>>> the next mapping is acquired. That way the ACPI code can be fixed
>>> gradually and without breaking existing functionality.
>>>
>>
>> ok, i stuck in your patches into tip/master today and -tip testing
>> quickly found an early-ioremap leak:
>>
>> [   36.625100] calling  check_early_ioremap_leak+0x0/0x3d
>> [   36.630253] ------------[ cut here ]------------
>> [   36.634884] WARNING: at arch/x86/mm/ioremap.c:577 check_early_ioremap_leak+0x28/0x3d()
>> [   36.642811] Debug warning: early ioremap leak of 1 areas detected.
>>
>> find the full log below with ioremap-leak-tracing turned on. I've
>> excluded these commits for now from tip/master.
>>
>
> Yes, that leak is expected, unfortunately.  __acpi_map_table() has no
> corresponding unmap, and only maintains one mapping.  So it will leak
> its last mapping when it switches over from using __acpi_map_table() to
> ioremap().
>
> So, yes, its ugly, but its guaranteed to be a single leaked mapping.
> But I'm not sure what the best approach to deal with it is.
>
> (All those other backtraces are just informational, right?)
>

acpi_os_map_memory is the only user for __acpi_map_table (except es7000_32.c)

void __iomem *__init_refok
acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
{
        if (phys > ULONG_MAX) {
                printk(KERN_ERR PREFIX "Cannot map memory that high\n");
                return NULL;
        }
        if (acpi_gbl_permanent_mmap)
                /*
                * ioremap checks to ensure this is in reserved space
                */
                return ioremap((unsigned long)phys, size);
        else
                return __acpi_map_table((unsigned long)phys, size);
}
EXPORT_SYMBOL_GPL(acpi_os_map_memory);

void acpi_os_unmap_memory(void __iomem * virt, acpi_size size)
{
        if (acpi_gbl_permanent_mmap) {
                iounmap(virt);
        }
}
EXPORT_SYMBOL_GPL(acpi_os_unmap_memory);

just let acpi_os_unmap_memory to call __acpi_unmap_table...

YH
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