Merge tag 'v4.3-rc6' into locking/core, to pick up fixes before applying new changes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 16 insertions, 18 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 72940fb..1cc5467 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2473,6 +2473,21 @@ 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;
+		}
+
 		status = a_ops->write_begin(file, mapping, pos, bytes, flags,
 						&page, &fsdata);
 		if (unlikely(status < 0))
@@ -2480,17 +2495,8 @@ 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,
@@ -2513,14 +2519,6 @@ 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;