Merge branch 'Don't reinit map value in prealloc_lru_pop'

Kumar Kartikeya Dwivedi says:

====================

Fix for a bug in prealloc_lru_pop spotted while reading the code, then a test +
example that checks whether it is fixed.

Changelog:
----------
v2 -> v3:
v2: https://lore.kernel.org/bpf/20220809140615.21231-1-memxor@gmail.com

 * Switch test to use kptr instead of kptr_ref to stabilize test runs
 * Fix missing lru_bug__destroy (Yonghong)
 * Collect Acks

v1 -> v2:
v1: https://lore.kernel.org/bpf/20220806014603.1771-1-memxor@gmail.com

 * Expand commit log to include summary of the discussion with Yonghong
 * Make lru_bug selftest serial to not mess up refcount for map_kptr test
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 49 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/lru_bug.c b/tools/testing/selftests/bpf/progs/lru_bug.c
new file mode 100644
index 000000000000..687081a724b3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/lru_bug.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+struct map_value {
+	struct task_struct __kptr *ptr;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_LRU_HASH);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct map_value);
+} lru_map SEC(".maps");
+
+int pid = 0;
+int result = 1;
+
+SEC("fentry/bpf_ktime_get_ns")
+int printk(void *ctx)
+{
+	struct map_value v = {};
+
+	if (pid == bpf_get_current_task_btf()->pid)
+		bpf_map_update_elem(&lru_map, &(int){0}, &v, 0);
+	return 0;
+}
+
+SEC("fentry/do_nanosleep")
+int nanosleep(void *ctx)
+{
+	struct map_value val = {}, *v;
+	struct task_struct *current;
+
+	bpf_map_update_elem(&lru_map, &(int){0}, &val, 0);
+	v = bpf_map_lookup_elem(&lru_map, &(int){0});
+	if (!v)
+		return 0;
+	bpf_map_delete_elem(&lru_map, &(int){0});
+	current = bpf_get_current_task_btf();
+	v->ptr = current;
+	pid = current->pid;
+	bpf_ktime_get_ns();
+	result = !v->ptr;
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";