Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

[karo-tx-linux.git] / mm / filemap.c

diff --git a/mm/filemap.c b/mm/filemap.c
index 72940fb38666811b80c146bc085a1c84fc0e7ecc..1cc5467cf36ce7852f7a0474d5fd3237b3dfff10 100644 (file)
--- 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;