linux-kernel - [PATCH bpf-next] selftests/bpf: fix potential premature unload in bpf

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Message-ID: <20240109164317.16371-1-asavkov@redhat.com>
Date: Tue,  9 Jan 2024 17:43:17 +0100
From: Artem Savkov <asavkov@...hat.com>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	jolsa@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Artem Savkov <asavkov@...hat.com>
Subject: [PATCH bpf-next] selftests/bpf: fix potential premature unload in bpf_testmod

It is possible for bpf_kfunc_call_test_release() to be called from
bpf_map_free_deferred() when bpf_testmod is already unloaded and
perf_test_stuct.cnt which it tries to decrease is no longer in memory.
This patch tries to fix the issue by waiting for all references to be
dropped in bpf_testmod_exit().

The issue can be triggered by running 'test_progs -t map_kptr' in 6.5,
but is obscured in 6.6 by d119357d07435 ("rcu-tasks: Treat only
synchronous grace periods urgently").

Fixes: 65eb006d85a2a ("bpf: Move kernel test kfuncs to bpf_testmod")
---
 tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 91907b321f913..63f0dbd016703 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -2,6 +2,7 @@
 /* Copyright (c) 2020 Facebook */
 #include <linux/btf.h>
 #include <linux/btf_ids.h>
+#include <linux/delay.h>
 #include <linux/error-injection.h>
 #include <linux/init.h>
 #include <linux/module.h>
@@ -544,6 +545,9 @@ static int bpf_testmod_init(void)
 
 static void bpf_testmod_exit(void)
 {
+	while (refcount_read(&prog_test_struct.cnt) > 1)
+		msleep(20);
+
 	return sysfs_remove_bin_file(kernel_kobj, &bin_attr_bpf_testmod_file);
 }
 
-- 
2.43.0