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>

1 files changed, 13 insertions, 9 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 81d7117aa58b..e046b7e4b530 100644
--- 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;