Messages in this thread Patch in this message | | | Date | Thu, 23 Jan 2014 20:27:29 +0400 (MSK) | From | malc <> | Subject | [PATCH] Revert "mm/vmalloc: interchage the implementation of vmalloc_to_{pfn,page}" |
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Sep 17 00:00:00 2001 From: Vladimir Murzin <murzin.v@gmail.com> Date: Thu, 23 Jan 2014 14:54:20 +0400 Subject: [PATCH] Revert "mm/vmalloc: interchage the implementation of vmalloc_to_{pfn,page}"
This reverts commit ece86e222db48d04bda218a2be70e384518bb08c.
Despite being claimed that 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> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> ---
I'm a bit surprised to see this patch merged because I've already pointed [1] at difference in behaviour introduced by the patch.
If I've lost the point here or misunderstand the patch or abuse vmalloc_to_* interface I'd be grateful if someone let me know.
[1] https://lkml.org/lkml/2013/12/1/76
Thanks Vladimir
mm/vmalloc.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index e4f0db2..0fdf968 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -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 ***/ -- 1.7.10.4
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