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Subject: Re: PAT wc & vmap mapping count issue ?
From: Jerome Glisse <glisse@freedesktop.org>
To: linux-kernel@vger.kernel.org
Cc: venkatesh.pallipadi@intel.com
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Date: Thu, 30 Jul 2009 19:06:33 +0200
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On Thu, 2009-07-30 at 13:11 +0200, Jerome Glisse wrote:
> Hello,
> 
> I think i am facing a PAT issue code (at bottom of the mail) leads
> to mapping count issue such as one at bottom of mail. Is my test
> code buggy ? If so what is wrong with it ? Otherwise how could i
> track this down ? (Tested with lastest Linus tree). Note that
> the mapping count sometimes is negative, sometimes it's positive
> but without proper mapping.
> 
> (With AMD Athlon(tm) Dual Core Processor 4450e)
> 
> Note that bad page might takes time to happen 256 pages is bit
> too little either increasing that or doing memory hungry task
> will helps triggering the bug faster.
> 
> Cheers,
> Jerome
> 
> Jul 30 11:12:36 localhost kernel: BUG: Bad page state in process bash
> pfn:6daed
> Jul 30 11:12:36 localhost kernel: page:ffffea0001b6bb40
> flags:4000000000000000 count:1 mapcount:1 mapping:(null) index:6d8
> Jul 30 11:12:36 localhost kernel: Pid: 1876, comm: bash Not tainted
> 2.6.31-rc2 #30
> Jul 30 11:12:36 localhost kernel: Call Trace:
> Jul 30 11:12:36 localhost kernel: [<ffffffff81098570>] bad_page
> +0xf8/0x10d
> Jul 30 11:12:36 localhost kernel: [<ffffffff810997aa>]
> get_page_from_freelist+0x357/0x475
> Jul 30 11:12:36 localhost kernel: [<ffffffff810a72e3>] ? cond_resched
> +0x9/0xb
> Jul 30 11:12:36 localhost kernel: [<ffffffff810a9958>] ? copy_page_range
> +0x4cc/0x558
> Jul 30 11:12:36 localhost kernel: [<ffffffff810999e0>]
> __alloc_pages_nodemask+0x118/0x562
> Jul 30 11:12:36 localhost kernel: [<ffffffff812a92c3>] ?
> _spin_unlock_irq+0xe/0x11
> Jul 30 11:12:36 localhost kernel: [<ffffffff810a9dda>]
> alloc_pages_node.clone.0+0x14/0x16
> Jul 30 11:12:36 localhost kernel: [<ffffffff810aa0b1>] do_wp_page
> +0x2d5/0x57d
> Jul 30 11:12:36 localhost kernel: [<ffffffff810aac00>] handle_mm_fault
> +0x586/0x5e0
> Jul 30 11:12:36 localhost kernel: [<ffffffff812ab635>] do_page_fault
> +0x20a/0x21f
> Jul 30 11:12:36 localhost kernel: [<ffffffff812a968f>] page_fault
> +0x1f/0x30
> Jul 30 11:12:36 localhost kernel: Disabling lock debugging due to kernel
> taint
> 
> #define NPAGEST 256
> void test_wc(void)
> {
>         struct page *pages[NPAGEST];
>         int i, j;
>         void *virt;
> 
>         for (i = 0; i < NPAGEST; i++) {
>                 pages[i] = NULL;
>         }
>         for (i = 0; i < NPAGEST; i++) {
>                 pages[i] = alloc_page(__GFP_DMA32 | GFP_USER);
>                 if (pages[i] == NULL) {
>                         printk(KERN_ERR "Failled allocating page %d\n",
> i);
>                         goto out_free;
>                 }
>                 if (!PageHighMem(pages[i]))
>                         if (set_memory_wc((unsigned long)
> page_address(pages[i]), 1)) {
>                                 printk(KERN_ERR "Failled setting page %d
> wc\n", i);
>                                 goto out_free;
>                         }
>         }
>         virt = vmap(pages, NPAGEST, 0,
> pgprot_writecombine(PAGE_KERNEL));
>         if (virt == NULL) {
>                 printk(KERN_ERR "Failled vmapping\n");
>                 goto out_free;
>         }
>         vunmap(virt);
> out_free:
>         for (i = 0; i < NPAGEST; i++) {
>                 if (pages[i]) {
>                         if (!PageHighMem(pages[i]))
>                                 set_memory_wb((unsigned long)
> page_address(pages[i]), 1);
>                         __free_page(pages[i]);
>                 }
>         }
> }

vmaping doesn't seems to be involved with the corruption simply
setting some pages with set_memory_wc is enough.

Cheers,
Jerome

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