fs/backing-file: Convert to revert/override_creds_light()

As the credentials used by backing-file are long lived in relation to
the critical section (override_creds() -> revert_creds()) we can
replace them by their lighter alternatives.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

fs/backing-file.c

@@ -176,7 +176,7 @@ ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
 	    !(file->f_mode & FMODE_CAN_ODIRECT))
 		return -EINVAL;
 
-	old_cred = override_creds(ctx->cred);
+	old_cred = override_creds_light(ctx->cred);
 	if (is_sync_kiocb(iocb)) {
 		rwf_t rwf = iocb_to_rw_flags(flags);
 
@@ -197,7 +197,7 @@ ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
 			backing_aio_cleanup(aio, ret);
 	}
 out:
-	revert_creds(old_cred);
+	revert_creds_light(old_cred);
 
 	if (ctx->accessed)
 		ctx->accessed(iocb->ki_filp);
@@ -233,7 +233,7 @@ ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
 	 */
 	flags &= ~IOCB_DIO_CALLER_COMP;
 
-	old_cred = override_creds(ctx->cred);
+	old_cred = override_creds_light(ctx->cred);
 	if (is_sync_kiocb(iocb)) {
 		rwf_t rwf = iocb_to_rw_flags(flags);
 
@@ -264,7 +264,7 @@ ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
 			backing_aio_cleanup(aio, ret);
 	}
 out:
-	revert_creds(old_cred);
+	revert_creds_light(old_cred);
 
 	return ret;
 }
@@ -281,9 +281,9 @@ ssize_t backing_file_splice_read(struct file *in, struct kiocb *iocb,
 	if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING)))
 		return -EIO;
 
-	old_cred = override_creds(ctx->cred);
+	old_cred = override_creds_light(ctx->cred);
 	ret = vfs_splice_read(in, &iocb->ki_pos, pipe, len, flags);
-	revert_creds(old_cred);
+	revert_creds_light(old_cred);
 
 	if (ctx->accessed)
 		ctx->accessed(iocb->ki_filp);
@@ -310,11 +310,11 @@ ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
 	if (ret)
 		return ret;
 
-	old_cred = override_creds(ctx->cred);
+	old_cred = override_creds_light(ctx->cred);
 	file_start_write(out);
 	ret = out->f_op->splice_write(pipe, out, &iocb->ki_pos, len, flags);
 	file_end_write(out);
-	revert_creds(old_cred);
+	revert_creds_light(old_cred);
 
 	if (ctx->end_write)
 		ctx->end_write(iocb, ret);
@@ -337,9 +337,9 @@ int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
 
 	vma_set_file(vma, file);
 
-	old_cred = override_creds(ctx->cred);
+	old_cred = override_creds_light(ctx->cred);
 	ret = call_mmap(vma->vm_file, vma);
-	revert_creds(old_cred);
+	revert_creds_light(old_cred);
 
 	if (ctx->accessed)
 		ctx->accessed(vma->vm_file);