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Revert "mm/vmalloc: interchage the implementation of vmalloc_to_{pfn,page}"

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Revert commit ece86e222db4, which was intended as a small performance
improvement.

Despite the claim that the patch doesn't introduce any functional
changes in fact it does.

The "no page" path behaves different now.  Originally, vmalloc_to_page
might return NULL under some conditions, with new implementation it
returns pfn_to_page(0) which is not the same as NULL.

Simple test shows the difference.

test.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>

int __init myi(void)
{
	struct page *p;
	void *v;

	v = vmalloc(PAGE_SIZE);
	/* trigger the "no page" path in vmalloc_to_page*/
	vfree(v);

	p = vmalloc_to_page(v);

	pr_err("expected val = NULL, returned val = %p", p);

	return -EBUSY;
}

void __exit mye(void)
{

}
module_init(myi)
module_exit(mye)

Before interchange:
expected val = NULL, returned val =   (null)

After interchange:
expected val = NULL, returned val = c7ebe000

Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
Cc: Jianyu Zhan <nasa4836@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
malc 2014-01-27 17:06:53 -08:00 committed by Linus Torvalds
parent fb5bb60cd0
commit add688fbd3
1 changed files with 14 additions and 14 deletions
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28
mm/vmalloc.c
View File

@ -220,12 +220,12 @@ int is_vmalloc_or_module_addr(const void *x)
}
/*
* Walk a vmap address to the physical pfn it maps to.
* Walk a vmap address to the struct page it maps.
*/
unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
struct page *vmalloc_to_page(const void *vmalloc_addr)
{
unsigned long addr = (unsigned long) vmalloc_addr;
unsigned long pfn = 0;
struct page *page = NULL;
pgd_t *pgd = pgd_offset_k(addr);
/*
@ -244,24 +244,24 @@ unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
ptep = pte_offset_map(pmd, addr);
pte = *ptep;
if (pte_present(pte))
pfn = pte_pfn(pte);
page = pte_page(pte);
pte_unmap(ptep);
}
}
}
return pfn;
}
EXPORT_SYMBOL(vmalloc_to_pfn);
/*
* Map a vmalloc()-space virtual address to the struct page.
*/
struct page *vmalloc_to_page(const void *vmalloc_addr)
{
return pfn_to_page(vmalloc_to_pfn(vmalloc_addr));
return page;
}
EXPORT_SYMBOL(vmalloc_to_page);
/*
* Map a vmalloc()-space virtual address to the physical page frame number.
*/
unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
{
return page_to_pfn(vmalloc_to_page(vmalloc_addr));
}
EXPORT_SYMBOL(vmalloc_to_pfn);
/*** Global kva allocator ***/