selftests/bpf: Fix arena_spin_lock compilation on PowerPC

Venkat reported a compilation error for BPF selftests on PowerPC [0].
The crux of the error is the following message:
  In file included from progs/arena_spin_lock.c:7:
  /root/bpf-next/tools/testing/selftests/bpf/bpf_arena_spin_lock.h:122:8:
  error: member reference base type '__attribute__((address_space(1)))
  u32' (aka '__attribute__((address_space(1))) unsigned int') is not a
  structure or union
     122 |         old = atomic_read(&lock->val);

This is because PowerPC overrides the qspinlock type changing the
lock->val member's type from atomic_t to u32.

To remedy this, import the asm-generic version in the arena spin lock
header, name it __qspinlock (since it's aliased to arena_spinlock_t, the
actual name hardly matters), and adjust the selftest to not depend on
the type in vmlinux.h.

  [0]: https://lore.kernel.org/bpf/7bc80a3b-d708-4735-aa3b-6a8c21720f9d@linux.ibm.com

Fixes: 88d706b ("selftests/bpf: Introduce arena spin lock")
Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Link: https://lore.kernel.org/bpf/20250311154244.3775505-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: kkdwivedi

tools/testing/selftests/bpf/bpf_arena_spin_lock.h

@@ -22,7 +22,28 @@
 
 extern unsigned long CONFIG_NR_CPUS __kconfig;
 
-#define arena_spinlock_t struct qspinlock
+/*
+ * Typically, we'd just rely on the definition in vmlinux.h for qspinlock, but
+ * PowerPC overrides the definition to define lock->val as u32 instead of
+ * atomic_t, leading to compilation errors.  Import a local definition below so
+ * that we don't depend on the vmlinux.h version.
+ */
+
+struct __qspinlock {
+	union {
+		atomic_t val;
+		struct {
+			u8 locked;
+			u8 pending;
+		};
+		struct {
+			u16 locked_pending;
+			u16 tail;
+		};
+	};
+};
+
+#define arena_spinlock_t struct __qspinlock
 /* FIXME: Using typedef causes CO-RE relocation error */
 /* typedef struct qspinlock arena_spinlock_t; */
 

tools/testing/selftests/bpf/prog_tests/arena_spin_lock.c

@@ -4,8 +4,8 @@
 #include <network_helpers.h>
 #include <sys/sysinfo.h>
 
-struct qspinlock { int val; };
-typedef struct qspinlock arena_spinlock_t;
+struct __qspinlock { int val; };
+typedef struct __qspinlock arena_spinlock_t;
 
 struct arena_qnode {
 	unsigned long next;