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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 Wed, 2014-05-21 at 14:35 -0600, Toshi Kani wrote:
> 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?

Hi Matthew,

The following change works in my environment. What do you think?

Thanks,
-Toshi

---
fs/dax.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/dax.c b/fs/dax.c
index 2d6b4bc..046c6d6 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -26,6 +26,7 @@
#include <linux/sched.h>
#include <linux/uio.h>
#include <linux/vmstat.h>
+#include <linux/rmap.h>

int dax_clear_blocks(struct inode *inode, sector_t block, long size)
{
@@ -385,6 +386,8 @@ static int do_dax_fault(struct vm_area_struct *vma,
struct vm_fault *vmf,
mutex_unlock(&mapping->i_mmap_mutex);

if (page) {
+ if (page_mapped(page))
+ try_to_unmap(page, TTU_UNMAP|TTU_IGNORE_ACCESS);
delete_from_page_cache(page);
unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
PAGE_CACHE_SIZE, 0);



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