selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 127 insertions, 0 deletions

diff --git a/tools/perf/util/sample.c b/tools/perf/util/sample.c
new file mode 100644
index 000000000..cf7332932
--- /dev/null
+++ b/tools/perf/util/sample.c
@@ -0,0 +1,127 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include "sample.h"
+#include "debug.h"
+#include "thread.h"
+#include <elf.h>
+#ifndef EM_CSKY
+#define EM_CSKY		252
+#endif
+#ifndef EM_LOONGARCH
+#define EM_LOONGARCH	258
+#endif
+#include <linux/zalloc.h>
+#include <stdlib.h>
+#include <string.h>
+#include "../../arch/x86/include/asm/insn.h"
+
+void perf_sample__init(struct perf_sample *sample, bool all)
+{
+	if (all) {
+		memset(sample, 0, sizeof(*sample));
+	} else {
+		sample->evsel = NULL;
+		sample->user_regs = NULL;
+		sample->intr_regs = NULL;
+		sample->merged_callchain = false;
+		sample->callchain = NULL;
+	}
+}
+
+void perf_sample__exit(struct perf_sample *sample)
+{
+	zfree(&sample->user_regs);
+	zfree(&sample->intr_regs);
+	if (sample->merged_callchain) {
+		zfree(&sample->callchain);
+		sample->merged_callchain = false;
+	}
+}
+
+struct regs_dump *perf_sample__user_regs(struct perf_sample *sample)
+{
+	if (!sample->user_regs) {
+		sample->user_regs = zalloc(sizeof(*sample->user_regs));
+		if (!sample->user_regs)
+			pr_err("Failure to allocate sample user_regs");
+	}
+	return sample->user_regs;
+}
+
+
+struct regs_dump *perf_sample__intr_regs(struct perf_sample *sample)
+{
+	if (!sample->intr_regs) {
+		sample->intr_regs = zalloc(sizeof(*sample->intr_regs));
+		if (!sample->intr_regs)
+			pr_err("Failure to allocate sample intr_regs");
+	}
+	return sample->intr_regs;
+}
+
+static int elf_machine_max_instruction_length(uint16_t e_machine)
+{
+	switch (e_machine) {
+	/* Fixed 4-byte (32-bit) architectures */
+	case EM_AARCH64:
+	case EM_PPC:
+	case EM_PPC64:
+	case EM_MIPS:
+	case EM_SPARC:
+	case EM_SPARCV9:
+	case EM_ALPHA:
+	case EM_LOONGARCH:
+	case EM_PARISC:
+	case EM_SH:
+		return 4;
+
+	/* Variable length or mixed-mode architectures */
+	case EM_ARM:    /* Variable due to Thumb/Thumb-2 */
+	case EM_RISCV:  /* Variable due to Compressed (C) extension */
+	case EM_CSKY:   /* Variable (16 or 32 bit) */
+	case EM_ARC:    /* Variable (ARCompact) */
+		return 4;
+	case EM_S390:   /* Variable (2, 4, or 6 bytes) */
+		return 6;
+	case EM_68K:
+		return 10;
+	case EM_386:
+	case EM_X86_64:
+		return 15;
+	case EM_XTENSA: /* Variable (FLIX) */
+		return 16;
+	default:
+		return MAX_INSN;
+	}
+}
+
+void perf_sample__fetch_insn(struct perf_sample *sample,
+			     struct thread *thread,
+			     struct machine *machine)
+{
+	int ret, len;
+	bool is64bit = false;
+	uint16_t e_machine;
+
+	if (!sample->ip || sample->insn_len != 0)
+		return;
+
+	e_machine = thread__e_machine(thread, machine, /*e_flags=*/NULL);
+	len = elf_machine_max_instruction_length(e_machine);
+	len = thread__memcpy(thread, machine, sample->insn,
+			     sample->ip, len,
+			     &is64bit);
+	if (len <= 0)
+		return;
+
+	sample->insn_len = len;
+
+	if (e_machine == EM_386 || e_machine == EM_X86_64) {
+		/* Refine the x86 instruction length with the decoder. */
+		struct insn insn;
+
+		ret = insn_decode(&insn, sample->insn, len,
+				  is64bit ? INSN_MODE_64 : INSN_MODE_32);
+		if (ret >= 0 && insn.length <= len)
+			sample->insn_len = insn.length;
+	}
+}