linux-kernel - Re: [PATCH v4 3.0-rc2-tip 2/22] 2: uprobes: Breakground page replacement.

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Message-ID: <1308228485.13240.61.camel@twins>
Date:	Thu, 16 Jun 2011 14:48:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jonathan Corbet <corbet@....net>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3.0-rc2-tip 2/22]  2: uprobes: Breakground page
 replacement.

On Tue, 2011-06-07 at 18:28 +0530, Srikar Dronamraju wrote:
> +static int __replace_page(struct vm_area_struct *vma, struct page *page,
> +                                       struct page *kpage)
> +{
> +       struct mm_struct *mm = vma->vm_mm;
> +       pgd_t *pgd;
> +       pud_t *pud;
> +       pmd_t *pmd;
> +       pte_t *ptep;
> +       spinlock_t *ptl;
> +       unsigned long addr;
> +       int err = -EFAULT;
> +
> +       addr = page_address_in_vma(page, vma);
> +       if (addr == -EFAULT)
> +               goto out;
> +
> +       pgd = pgd_offset(mm, addr);
> +       if (!pgd_present(*pgd))
> +               goto out;
> +
> +       pud = pud_offset(pgd, addr);
> +       if (!pud_present(*pud))
> +               goto out;
> +
> +       pmd = pmd_offset(pud, addr);
> +       if (pmd_trans_huge(*pmd) || (!pmd_present(*pmd)))
> +               goto out;
> +
> +       ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
> +       if (!ptep)
> +               goto out;

Shouldn't we verify that the obtained pte does indeed refer to our @page
here?

> +       get_page(kpage);
> +       page_add_new_anon_rmap(kpage, vma, addr);
> +
> +       flush_cache_page(vma, addr, pte_pfn(*ptep));
> +       ptep_clear_flush(vma, addr, ptep);
> +       set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
> +
> +       page_remove_rmap(page);
> +       if (!page_mapped(page))
> +               try_to_free_swap(page);
> +       put_page(page);
> +       pte_unmap_unlock(ptep, ptl);
> +       err = 0;
> +
> +out:
> +       return err;
> +} 

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