selftests/bpf: Fix map_kptr grace period wait

Commit c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")
broke map_kptr selftest since it removed the function we were kprobing.
Use a new kfunc that invokes call_rcu_tasks_trace and sets a program
provided pointer to an integer to 1. Technically this can be unsafe if
the memory being written to from the callback disappears, but this is
just for usage in a test where we ensure we spin until we see the value
to be set to 1, so it's ok.

Reported-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Fixes: c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260211185747.3630539-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 29 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index 186a25ab429a..e62c6b78657f 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -18,6 +18,7 @@
 #include <linux/in6.h>
 #include <linux/un.h>
 #include <linux/filter.h>
+#include <linux/rcupdate_trace.h>
 #include <net/sock.h>
 #include <linux/namei.h>
 #include "bpf_testmod.h"
@@ -885,6 +886,32 @@ __bpf_kfunc void bpf_kfunc_call_test_sleepable(void)
 {
 }
 
+struct bpf_kfunc_rcu_tasks_trace_data {
+	struct rcu_head rcu;
+	int *done;
+};
+
+static void bpf_kfunc_rcu_tasks_trace_cb(struct rcu_head *rhp)
+{
+	struct bpf_kfunc_rcu_tasks_trace_data *data;
+
+	data = container_of(rhp, struct bpf_kfunc_rcu_tasks_trace_data, rcu);
+	WRITE_ONCE(*data->done, 1);
+	kfree(data);
+}
+
+__bpf_kfunc int bpf_kfunc_call_test_call_rcu_tasks_trace(int *done)
+{
+	struct bpf_kfunc_rcu_tasks_trace_data *data;
+
+	data = kmalloc(sizeof(*data), GFP_ATOMIC);
+	if (!data)
+		return -ENOMEM;
+	data->done = done;
+	call_rcu_tasks_trace(&data->rcu, bpf_kfunc_rcu_tasks_trace_cb);
+	return 0;
+}
+
 __bpf_kfunc int bpf_kfunc_init_sock(struct init_sock_args *args)
 {
 	int proto;
@@ -1222,6 +1249,7 @@ BTF_ID_FLAGS(func, bpf_kfunc_call_test_destructive, KF_DESTRUCTIVE)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test_static_unused_arg)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test_offset)
 BTF_ID_FLAGS(func, bpf_kfunc_call_test_sleepable, KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_kfunc_call_test_call_rcu_tasks_trace)
 BTF_ID_FLAGS(func, bpf_kfunc_init_sock, KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_kfunc_close_sock, KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_kfunc_call_kernel_connect, KF_SLEEPABLE)
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
index d5c5454e257e..b393bf771131 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h
@@ -118,6 +118,7 @@ void bpf_kfunc_call_test_mem_len_fail2(__u64 *mem, int len) __ksym;
 
 void bpf_kfunc_call_test_destructive(void) __ksym;
 void bpf_kfunc_call_test_sleepable(void) __ksym;
+int bpf_kfunc_call_test_call_rcu_tasks_trace(int *done) __ksym;
 
 void bpf_kfunc_call_test_offset(struct prog_test_ref_kfunc *p);
 struct prog_test_member *bpf_kfunc_call_memb_acquire(void);