Provide a helper function for finishing write faults due to PTE being
read-only. The helper will be used by DAX to avoid the need of
complicating generic MM code with DAX locking specifics.
Signed-off-by: Jan Kara <j...@suse.cz>
---
include/linux/mm.h | 1 +
mm/memory.c | 65 +++++++++++++++++++++++++++++++-----------------------
2 files changed, 39 insertions(+), 27 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1055f2ece80d..e5a014be8932 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -617,6 +617,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct
vm_area_struct *vma)
int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
struct page *page);
int finish_fault(struct vm_fault *vmf);
+int finish_mkwrite_fault(struct vm_fault *vmf);
#endif
/*
diff --git a/mm/memory.c b/mm/memory.c
index f49e736d6a36..8c8cb7f2133e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2266,6 +2266,36 @@ oom:
return VM_FAULT_OOM;
}
+/**
+ * finish_mkrite_fault - finish page fault making PTE writeable once the page
+ * page is prepared
+ *
+ * @vmf: structure describing the fault
+ *
+ * This function handles all that is needed to finish a write page fault due
+ * to PTE being read-only once the mapped page is prepared. It handles locking
+ * of PTE and modifying it. The function returns VM_FAULT_WRITE on success,
+ * 0 when PTE got changed before we acquired PTE lock.
+ *
+ * The function expects the page to be locked or other protection against
+ * concurrent faults / writeback (such as DAX radix tree locks).
+ */
+int finish_mkwrite_fault(struct vm_fault *vmf)
+{
+ vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address,
+ &vmf->ptl);
+ /*
+ * We might have raced with another page fault while we released the
+ * pte_offset_map_lock.
+ */
+ if (!pte_same(*vmf->pte, vmf->orig_pte)) {
+ pte_unmap_unlock(vmf->pte, vmf->ptl);
+ return 0;
+ }
+ wp_page_reuse(vmf);
+ return VM_FAULT_WRITE;
+}
+
/*
* Handle write page faults for VM_MIXEDMAP or VM_PFNMAP for a VM_SHARED
* mapping
@@ -2282,16 +2312,7 @@ static int wp_pfn_shared(struct vm_fault *vmf)
ret = vma->vm_ops->pfn_mkwrite(vma, vmf);
if (ret & VM_FAULT_ERROR)
return ret;
- vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
- vmf->address, &vmf->ptl);
- /*
- * We might have raced with another page fault while we
- * released the pte_offset_map_lock.
- */
- if (!pte_same(*vmf->pte, vmf->orig_pte)) {
- pte_unmap_unlock(vmf->pte, vmf->ptl);
- return 0;
- }
+ return finish_mkwrite_fault(vmf);
}
wp_page_reuse(vmf);
return VM_FAULT_WRITE;
@@ -2301,7 +2322,6 @@ static int wp_page_shared(struct vm_fault *vmf)
__releases(vmf->ptl)
{
struct vm_area_struct *vma = vmf->vma;
- int page_mkwrite = 0;
get_page(vmf->page);
@@ -2315,26 +2335,17 @@ static int wp_page_shared(struct vm_fault *vmf)
put_page(vmf->page);
return tmp;
}
- /*
- * Since we dropped the lock we need to revalidate
- * the PTE as someone else may have changed it. If
- * they did, we just return, as we can count on the
- * MMU to tell us if they didn't also make it writable.
- */
- vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
- vmf->address, &vmf->ptl);
- if (!pte_same(*vmf->pte, vmf->orig_pte)) {
+ tmp = finish_mkwrite_fault(vmf);
+ if (unlikely(!tmp || (tmp &
+ (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
unlock_page(vmf->page);
- pte_unmap_unlock(vmf->pte, vmf->ptl);
put_page(vmf->page);
- return 0;
+ return tmp;
}
- page_mkwrite = 1;
- }
-
- wp_page_reuse(vmf);
- if (!page_mkwrite)
+ } else {
+ wp_page_reuse(vmf);
lock_page(vmf->page);
+ }
fault_dirty_shared_page(vma, vmf->page);
put_page(vmf->page);
--
2.6.6
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