1 files changed, 30 insertions, 5 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index bdc5d3c0977d..070aad543382 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -140,8 +140,7 @@ static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
 	struct page *page = buf->page;
 
 	if (page_count(page) == 1) {
-		if (memcg_kmem_enabled())
-			memcg_kmem_uncharge(page, 0);
+		memcg_kmem_uncharge(page, 0);
 		__SetPageLocked(page);
 		return 0;
 	}
@@ -226,8 +225,15 @@ void generic_pipe_buf_release(struct pipe_inode_info *pipe,
 }
 EXPORT_SYMBOL(generic_pipe_buf_release);
 
+/* New data written to a pipe may be appended to a buffer with this type. */
 static const struct pipe_buf_operations anon_pipe_buf_ops = {
-	.can_merge = 1,
+	.confirm = generic_pipe_buf_confirm,
+	.release = anon_pipe_buf_release,
+	.steal = anon_pipe_buf_steal,
+	.get = generic_pipe_buf_get,
+};
+
+static const struct pipe_buf_operations anon_pipe_buf_nomerge_ops = {
 	.confirm = generic_pipe_buf_confirm,
 	.release = anon_pipe_buf_release,
 	.steal = anon_pipe_buf_steal,
@@ -235,13 +241,32 @@ static const struct pipe_buf_operations anon_pipe_buf_ops = {
 };
 
 static const struct pipe_buf_operations packet_pipe_buf_ops = {
-	.can_merge = 0,
 	.confirm = generic_pipe_buf_confirm,
 	.release = anon_pipe_buf_release,
 	.steal = anon_pipe_buf_steal,
 	.get = generic_pipe_buf_get,
 };
 
+/**
+ * pipe_buf_mark_unmergeable - mark a &struct pipe_buffer as unmergeable
+ * @buf:	the buffer to mark
+ *
+ * Description:
+ *	This function ensures that no future writes will be merged into the
+ *	given &struct pipe_buffer. This is necessary when multiple pipe buffers
+ *	share the same backing page.
+ */
+void pipe_buf_mark_unmergeable(struct pipe_buffer *buf)
+{
+	if (buf->ops == &anon_pipe_buf_ops)
+		buf->ops = &anon_pipe_buf_nomerge_ops;
+}
+
+static bool pipe_buf_can_merge(struct pipe_buffer *buf)
+{
+	return buf->ops == &anon_pipe_buf_ops;
+}
+
 static ssize_t
 pipe_read(struct kiocb *iocb, struct iov_iter *to)
 {
@@ -379,7 +404,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 		struct pipe_buffer *buf = pipe->bufs + lastbuf;
 		int offset = buf->offset + buf->len;
 
-		if (buf->ops->can_merge && offset + chars <= PAGE_SIZE) {
+		if (pipe_buf_can_merge(buf) && offset + chars <= PAGE_SIZE) {
 			ret = pipe_buf_confirm(pipe, buf);
 			if (ret)
 				goto out;