Commit add688fb authored Jan 27, 2014 by malc Committed by Linus Torvalds Jan 27, 2014

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



Revert commit ece86e22, 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>

parent fb5bb60c

mm/vmalloc.c

+10 −10

Original line number	Diff line number	Diff line
		@@ -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);

		/*
		@@ -244,23 +244,23 @@ 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;
		return page;
		}
		EXPORT_SYMBOL(vmalloc_to_pfn);
		EXPORT_SYMBOL(vmalloc_to_page);

		/*
		* Map a vmalloc()-space virtual address to the struct page.
		* Map a vmalloc()-space virtual address to the physical page frame number.
		*/
		struct page vmalloc_to_page(const void vmalloc_addr)
		unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
		{
		return pfn_to_page(vmalloc_to_pfn(vmalloc_addr));
		return page_to_pfn(vmalloc_to_page(vmalloc_addr));
		}
		EXPORT_SYMBOL(vmalloc_to_page);
		EXPORT_SYMBOL(vmalloc_to_pfn);


		/* Global kva allocator */