selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 98 insertions, 0 deletions

diff --git a/samples/rpmsg/Makefile b/samples/rpmsg/Makefile
new file mode 100644
index 000000000..ddf9a5d13
--- /dev/null
+++ b/samples/rpmsg/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SAMPLE_RPMSG_CLIENT) += rpmsg_client_sample.o
diff --git a/samples/rpmsg/rpmsg_client_sample.c b/samples/rpmsg/rpmsg_client_sample.c
new file mode 100644
index 000000000..ae5081662
--- /dev/null
+++ b/samples/rpmsg/rpmsg_client_sample.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Remote processor messaging - sample client driver
+ *
+ * Copyright (C) 2011 Texas Instruments, Inc.
+ * Copyright (C) 2011 Google, Inc.
+ *
+ * Ohad Ben-Cohen <ohad@wizery.com>
+ * Brian Swetland <swetland@google.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/rpmsg.h>
+
+#define MSG		"hello world!"
+
+static int count = 100;
+module_param(count, int, 0644);
+
+struct instance_data {
+	int rx_count;
+};
+
+static int rpmsg_sample_cb(struct rpmsg_device *rpdev, void *data, int len,
+						void *priv, u32 src)
+{
+	int ret;
+	struct instance_data *idata = dev_get_drvdata(&rpdev->dev);
+
+	dev_info(&rpdev->dev, "incoming msg %d (src: 0x%x)\n",
+		 ++idata->rx_count, src);
+
+	print_hex_dump_debug(__func__, DUMP_PREFIX_NONE, 16, 1, data, len,
+			     true);
+
+	/* samples should not live forever */
+	if (idata->rx_count >= count) {
+		dev_info(&rpdev->dev, "goodbye!\n");
+		return 0;
+	}
+
+	/* send a new message now */
+	ret = rpmsg_send(rpdev->ept, MSG, strlen(MSG));
+	if (ret)
+		dev_err(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
+
+	return 0;
+}
+
+static int rpmsg_sample_probe(struct rpmsg_device *rpdev)
+{
+	int ret;
+	struct instance_data *idata;
+
+	dev_info(&rpdev->dev, "new channel: 0x%x -> 0x%x!\n",
+					rpdev->src, rpdev->dst);
+
+	idata = devm_kzalloc(&rpdev->dev, sizeof(*idata), GFP_KERNEL);
+	if (!idata)
+		return -ENOMEM;
+
+	dev_set_drvdata(&rpdev->dev, idata);
+
+	/* send a message to our remote processor */
+	ret = rpmsg_send(rpdev->ept, MSG, strlen(MSG));
+	if (ret) {
+		dev_err(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void rpmsg_sample_remove(struct rpmsg_device *rpdev)
+{
+	dev_info(&rpdev->dev, "rpmsg sample client driver is removed\n");
+}
+
+static struct rpmsg_device_id rpmsg_driver_sample_id_table[] = {
+	{ .name	= "rpmsg-client-sample" },
+	{ },
+};
+MODULE_DEVICE_TABLE(rpmsg, rpmsg_driver_sample_id_table);
+
+static struct rpmsg_driver rpmsg_sample_client = {
+	.drv.name	= KBUILD_MODNAME,
+	.id_table	= rpmsg_driver_sample_id_table,
+	.probe		= rpmsg_sample_probe,
+	.callback	= rpmsg_sample_cb,
+	.remove		= rpmsg_sample_remove,
+};
+module_rpmsg_driver(rpmsg_sample_client);
+
+MODULE_DESCRIPTION("Remote processor messaging sample client driver");
+MODULE_LICENSE("GPL v2");