linux-kernel - Re: [PATCH v7 07/22] Replace the XIP page fault handler with the DAX page fault handler

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Date:	Wed, 21 May 2014 14:35:07 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, willy@...ux.intel.com
Subject: Re: [PATCH v7 07/22] Replace the XIP page fault handler with the
 DAX page fault handler

On Sun, 2014-03-23 at 15:08 -0400, Matthew Wilcox wrote:
 :
> +static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> +			get_block_t get_block)
> +{
 :
> +	error = dax_get_pfn(inode, &bh, &pfn);
> +	if (error > 0)
> +		error = vm_insert_mixed(vma, vaddr, pfn);
> +	mutex_unlock(&mapping->i_mmap_mutex);
> +
> +	if (page) {
> +		delete_from_page_cache(page);
> +		unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
> +							PAGE_CACHE_SIZE, 0);
> +		unlock_page(page);
> +		page_cache_release(page);

Hi Matthew,

I am seeing a problem in this code path, where it deletes a page cache
page mapped to a hole. Sometimes, page->_mapcount is 0, not -1, which
leads __delete_from_page_cache(), called from delete_from_page_cache(),
to hit the following BUG_ON.

  BUG_ON(page_mapped(page))

I suppose such page has a shared mapping. Does this code need to take
care of replacing shared mappings in such case?

Thanks,
-Toshi



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