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.
Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
include/linux/mm.h | 1 +
mm/memory.c | 67 ++++++++++++++++++++++++++++++++----------------------
2 files changed, 41 insertions(+), 27 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 56fdd79e5d1e..0920adb6ec1b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -615,6 +615,7 @@ 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 06aba4203104..1517ff91c743 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2270,6 +2270,38 @@ static int wp_page_copy(struct vm_fault *vmf)
return VM_FAULT_OOM;
}
+/**
+ * finish_mkwrite_fault - finish page fault for a shared mapping, making PTE
+ * writeable once the page is prepared
+ *
+ * @vmf: structure describing the fault
+ *
+ * This function handles all that is needed to finish a write page fault in a
+ * shared mapping 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)
+{
+ WARN_ON_ONCE(!(vmf->vma->vm_flags & VM_SHARED));
+ 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
@@ -2286,16 +2318,7 @@ 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;
@@ -2305,7 +2328,6 @@ 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);
@@ -2319,26 +2341,17 @@ 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
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
