1 files changed, 21 insertions, 22 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 72940fb38666..327910c2400c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2473,6 +2473,26 @@ ssize_t generic_perform_write(struct file *file,
                                                 iov_iter_count(i));
 
 again:
+                /*
+                 * Bring in the user page that we will copy from _first_.
+                 * Otherwise there's a nasty deadlock on copying from the
+                 * same page as we're writing to, without it being marked
+                 * up-to-date.
+                 *
+                 * Not only is this an optimisation, but it is also required
+                 * to check that the address is actually valid, when atomic
+                 * usercopies are used, below.
+                 */
+                if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
+                        status = -EFAULT;
+                        break;
+                }
+
+                if (fatal_signal_pending(current)) {
+                        status = -EINTR;
+                        break;
+                }
+
                 status = a_ops->write_begin(file, mapping, pos, bytes, flags,
                                                 &page, &fsdata);
                 if (unlikely(status < 0))
@@ -2480,17 +2500,8 @@ again:
 
                 if (mapping_writably_mapped(mapping))
                         flush_dcache_page(page);
-                /*
-                 * 'page' is now locked.  If we are trying to copy from a
-                 * mapping of 'page' in userspace, the copy might fault and
-                 * would need PageUptodate() to complete.  But, page can not be
-                 * made Uptodate without acquiring the page lock, which we hold.
-                 * Deadlock.  Avoid with pagefault_disable().  Fix up below with
-                 * iov_iter_fault_in_readable().
-                 */
-                pagefault_disable();
+
                 copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
-                pagefault_enable();
                 flush_dcache_page(page);
 
                 status = a_ops->write_end(file, mapping, pos, bytes, copied,
@@ -2513,24 +2524,12 @@ again:
                          */
                         bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
                                                 iov_iter_single_seg_count(i));
-                        /*
-                         * This is the fallback to recover if the copy from
-                         * userspace above faults.
-                         */
-                        if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
-                                status = -EFAULT;
-                                break;
-                        }
                         goto again;
                 }
                 pos += copied;
                 written += copied;
 
                 balance_dirty_pages_ratelimited(mapping);
-                if (fatal_signal_pending(current)) {
-                        status = -EINTR;
-                        break;
-                }
         } while (iov_iter_count(i));
 
         return written ? written : status;