selftests/bpf: Add a test for objects stuck in free_by_rcu_ttracegrafted

Delete all elements of BPF_F_NO_PREALLOC hash map in one batch. The first
free_bulk() starts RCU tasks trace GP and the rest of the elements are
freed while it's in flight. Wait for call_rcu_ttrace_in_progress to clear
in bpf_mem_cache of every cpu and check that free_by_rcu_ttrace and
waiting_for_gp_ttrace lists are empty.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20260930095920.601738-4-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/lib/memweight.c b/lib/memweight.c
new file mode 100644
index 000000000..94dd72cca
--- /dev/null
+++ b/lib/memweight.c
@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+#include <linux/bug.h>
+#include <linux/bitmap.h>
+
+/**
+ * memweight - count the total number of bits set in memory area
+ * @ptr: pointer to the start of the area
+ * @bytes: the size of the area
+ */
+size_t memweight(const void *ptr, size_t bytes)
+{
+	size_t ret = 0;
+	size_t longs;
+	const unsigned char *bitmap = ptr;
+
+	for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
+			bytes--, bitmap++)
+		ret += hweight8(*bitmap);
+
+	longs = bytes / sizeof(long);
+	if (longs) {
+		BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
+		ret += bitmap_weight((unsigned long *)bitmap,
+				longs * BITS_PER_LONG);
+		bytes -= longs * sizeof(long);
+		bitmap += longs * sizeof(long);
+	}
+	/*
+	 * The reason that this last loop is distinct from the preceding
+	 * bitmap_weight() call is to compute 1-bits in the last region smaller
+	 * than sizeof(long) properly on big-endian systems.
+	 */
+	for (; bytes > 0; bytes--, bitmap++)
+		ret += hweight8(*bitmap);
+
+	return ret;
+}
+EXPORT_SYMBOL(memweight);