Merge tag 'v4.3-rc1' into perf/core, to refresh the tree

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

1 files changed, 19 insertions, 17 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 1283fc825458..72940fb38666 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -674,7 +674,7 @@ struct page *__page_cache_alloc(gfp_t gfp)
 		do {
 			cpuset_mems_cookie = read_mems_allowed_begin();
 			n = cpuset_mem_spread_node();
-			page = alloc_pages_exact_node(n, gfp, 0);
+			page = __alloc_pages_node(n, gfp, 0);
 		} while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
 
 		return page;
@@ -2473,21 +2473,6 @@ 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))
@@ -2495,8 +2480,17 @@ 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,
@@ -2519,6 +2513,14 @@ 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;