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-rw-r--r--mm/filemap.c34
1 files changed, 16 insertions, 18 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 72940fb38666..1cc5467cf36c 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;