Re: [PATCH 2/7] userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support

[Mike Rapoport <rppt@linux.vnet.ibm.com>]

On Thu, Aug 04, 2016 at 05:37:16PM +0800, Hillf Danton wrote:
> > 
> > +int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
> > +			   pmd_t *dst_pmd,
> > +			   struct vm_area_struct *dst_vma,
> > +			   unsigned long dst_addr,
> > +			   unsigned long src_addr,
> > +			   struct page **pagep)
> > +{
> > +	struct inode *inode = file_inode(dst_vma->vm_file);
> > +	struct shmem_inode_info *info = SHMEM_I(inode);
> > +	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
> > +	struct address_space *mapping = inode->i_mapping;
> > +	gfp_t gfp = mapping_gfp_mask(mapping);
> > +	pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
> > +	struct mem_cgroup *memcg;
> > +	spinlock_t *ptl;
> > +	void *page_kaddr;
> > +	struct page *page;
> > +	pte_t _dst_pte, *dst_pte;
> > +	int ret;
> > +
> > +	if (!*pagep) {
> > +		ret = -ENOMEM;
> > +		if (shmem_acct_block(info->flags))
> > +			goto out;
> > +		if (sbinfo->max_blocks) {
> > +			if (percpu_counter_compare(&sbinfo->used_blocks,
> > +						   sbinfo->max_blocks) >= 0)
> > +				goto out_unacct_blocks;
> > +			percpu_counter_inc(&sbinfo->used_blocks);
> > +		}
> > +
> > +		page = shmem_alloc_page(gfp, info, pgoff);
> > +		if (!page)
> > +			goto out_dec_used_blocks;
> > +
> > +		page_kaddr = kmap_atomic(page);
> > +		ret = copy_from_user(page_kaddr, (const void __user *)src_addr,
> > +				     PAGE_SIZE);
> > +		kunmap_atomic(page_kaddr);
> > +
> > +		/* fallback to copy_from_user outside mmap_sem */
> > +		if (unlikely(ret)) {
> > +			*pagep = page;
> > +			/* don't free the page */
> > +			return -EFAULT;
> > +		}
> > +	} else {
> > +		page = *pagep;
> > +		*pagep = NULL;
> > +	}
> > +
> > +	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
> > +	if (dst_vma->vm_flags & VM_WRITE)
> > +		_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
> > +
> > +	ret = -EEXIST;
> > +	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
> > +	if (!pte_none(*dst_pte))
> > +		goto out_release_uncharge_unlock;
> > +
> > +	__SetPageUptodate(page);
> > +
> > +	ret = mem_cgroup_try_charge(page, dst_mm, gfp, &memcg,
> > +				    false);
> > +	if (ret)
> > +		goto out_release_uncharge_unlock;
> > +	ret = radix_tree_maybe_preload(gfp & GFP_RECLAIM_MASK);
> 
> You have to load radix tree without &ptl held.

Thanks, will fix.
 
> Hillf
> 

--
Sincerely yours,
Mike.

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