Fix up recent get_user_pages() handling

The VM_FAULT_WRITE thing is an extra bit, not a valid return value, and
has to be treated as such by get_user_pages().

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/mm/memory.c b/mm/memory.c
index 81d7117aa58b65ec7f93cef8e212a337735ba440..e046b7e4b53092bb879f8d183d24de36b3389d83 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -949,6 +949,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 
                        cond_resched_lock(&mm->page_table_lock);
                        while (!(page = follow_page(mm, start, write_access))) {
+                               int ret;
+
                                /*
                                 * Shortcut for anonymous pages. We don't want
                                 * to force the creation of pages tables for
@@ -961,16 +963,18 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                                        break;
                                }
                                spin_unlock(&mm->page_table_lock);
-                               switch (__handle_mm_fault(mm, vma, start,
-                                                       write_access)) {
-                               case VM_FAULT_WRITE:
-                                       /*
-                                        * do_wp_page has broken COW when
-                                        * necessary, even if maybe_mkwrite
-                                        * decided not to set pte_write
-                                        */
+                               ret = __handle_mm_fault(mm, vma, start, write_access);
+
+                               /*
+                                * The VM_FAULT_WRITE bit tells us that do_wp_page has
+                                * broken COW when necessary, even if maybe_mkwrite
+                                * decided not to set pte_write. We can thus safely do
+                                * subsequent page lookups as if they were reads.
+                                */
+                               if (ret & VM_FAULT_WRITE)
                                        write_access = 0;
-                                       /* FALLTHRU */
+                               
+                               switch (ret & ~VM_FAULT_WRITE) {
                                case VM_FAULT_MINOR:
                                        tsk->min_flt++;
                                        break;