On Thu, 23 Jan 2014 20:27:29 +0400 (MSK) malc <av1474@xxxxxxxx> wrote:
> Sep 17 00:00:00 2001
> From: Vladimir Murzin <murzin.v@xxxxxxxxx>
> 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
>
hm, yes, I suppose that's bad.
Rather than reverting the patch we could fix up vmalloc_to_pfn() and/or
vmalloc_to_page() to handle this situation. Did you try that?
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