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SubjectRe: [PATCH v7 07/22] Replace the XIP page fault handler with the DAX page fault handler
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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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