x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

3 files changed, 180 insertions, 0 deletions

diff --git a/tools/testing/selftests/kcmp/.gitignore b/tools/testing/selftests/kcmp/.gitignore
new file mode 100644
index 000000000..38ccdfe80
--- /dev/null
+++ b/tools/testing/selftests/kcmp/.gitignore
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+kcmp_test
+kcmp-test-file
diff --git a/tools/testing/selftests/kcmp/Makefile b/tools/testing/selftests/kcmp/Makefile
new file mode 100644
index 000000000..59a1e5379
--- /dev/null
+++ b/tools/testing/selftests/kcmp/Makefile
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0-only
+CFLAGS += $(KHDR_INCLUDES)
+
+TEST_GEN_PROGS := kcmp_test
+
+EXTRA_CLEAN := $(OUTPUT)/kcmp-test-file
+
+include ../lib.mk
+
diff --git a/tools/testing/selftests/kcmp/kcmp_test.c b/tools/testing/selftests/kcmp/kcmp_test.c
new file mode 100644
index 000000000..79aa438b7
--- /dev/null
+++ b/tools/testing/selftests/kcmp/kcmp_test.c
@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <limits.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <fcntl.h>
+#include <linux/unistd.h>
+#include <linux/kcmp.h>
+
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <sys/epoll.h>
+
+#include "kselftest.h"
+
+static long sys_kcmp(int pid1, int pid2, int type, unsigned long fd1, unsigned long fd2)
+{
+	return syscall(__NR_kcmp, pid1, pid2, type, fd1, fd2);
+}
+
+static const unsigned int duped_num = 64;
+
+int main(int argc, char **argv)
+{
+	const char kpath[] = "kcmp-test-file";
+	struct kcmp_epoll_slot epoll_slot;
+	struct epoll_event ev;
+	int pid1, pid2;
+	int pipefd[2];
+	int fd1, fd2;
+	int epollfd;
+	int status;
+	int fddup;
+
+	fd1 = open(kpath, O_RDWR | O_CREAT | O_TRUNC, 0644);
+	pid1 = getpid();
+
+	if (fd1 < 0) {
+		perror("Can't create file");
+		ksft_exit_fail();
+	}
+
+	if (pipe(pipefd)) {
+		perror("Can't create pipe");
+		ksft_exit_fail();
+	}
+
+	epollfd = epoll_create1(0);
+	if (epollfd < 0) {
+		perror("epoll_create1 failed");
+		ksft_exit_fail();
+	}
+
+	memset(&ev, 0xff, sizeof(ev));
+	ev.events = EPOLLIN | EPOLLOUT;
+
+	if (epoll_ctl(epollfd, EPOLL_CTL_ADD, pipefd[0], &ev)) {
+		perror("epoll_ctl failed");
+		ksft_exit_fail();
+	}
+
+	fddup = dup2(pipefd[1], duped_num);
+	if (fddup < 0) {
+		perror("dup2 failed");
+		ksft_exit_fail();
+	}
+
+	if (epoll_ctl(epollfd, EPOLL_CTL_ADD, fddup, &ev)) {
+		perror("epoll_ctl failed");
+		ksft_exit_fail();
+	}
+	close(fddup);
+
+	pid2 = fork();
+	if (pid2 < 0) {
+		perror("fork failed");
+		ksft_exit_fail();
+	}
+
+	if (!pid2) {
+		int pid2 = getpid();
+		int ret;
+
+		ksft_print_header();
+		ksft_set_plan(3);
+
+		fd2 = open(kpath, O_RDWR);
+		if (fd2 < 0) {
+			perror("Can't open file");
+			ksft_exit_fail();
+		}
+
+		/* An example of output and arguments */
+		printf("pid1: %6d pid2: %6d FD: %2ld FILES: %2ld VM: %2ld "
+		       "FS: %2ld SIGHAND: %2ld IO: %2ld SYSVSEM: %2ld "
+		       "INV: %2ld\n",
+		       pid1, pid2,
+		       sys_kcmp(pid1, pid2, KCMP_FILE,		fd1, fd2),
+		       sys_kcmp(pid1, pid2, KCMP_FILES,		0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_VM,		0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_FS,		0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_SIGHAND,	0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_IO,		0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_SYSVSEM,	0, 0),
+
+			/* This one should fail */
+		       sys_kcmp(pid1, pid2, KCMP_TYPES + 1,	0, 0));
+
+		/* This one should return same fd */
+		ret = sys_kcmp(pid1, pid2, KCMP_FILE, fd1, fd1);
+		if (ret) {
+			printf("FAIL: 0 expected but %d returned (%s)\n",
+				ret, strerror(errno));
+			ksft_inc_fail_cnt();
+			ret = -1;
+		} else {
+			printf("PASS: 0 returned as expected\n");
+			ksft_inc_pass_cnt();
+		}
+
+		/* Compare with self */
+		ret = sys_kcmp(pid1, pid1, KCMP_VM, 0, 0);
+		if (ret) {
+			printf("FAIL: 0 expected but %d returned (%s)\n",
+				ret, strerror(errno));
+			ksft_inc_fail_cnt();
+			ret = -1;
+		} else {
+			printf("PASS: 0 returned as expected\n");
+			ksft_inc_pass_cnt();
+		}
+
+		/* Compare epoll target */
+		epoll_slot = (struct kcmp_epoll_slot) {
+			.efd	= epollfd,
+			.tfd	= duped_num,
+			.toff	= 0,
+		};
+		ret = sys_kcmp(pid1, pid1, KCMP_EPOLL_TFD, pipefd[1],
+			       (unsigned long)(void *)&epoll_slot);
+		if (ret) {
+			printf("FAIL: 0 expected but %d returned (%s)\n",
+				ret, strerror(errno));
+			ksft_inc_fail_cnt();
+			ret = -1;
+		} else {
+			printf("PASS: 0 returned as expected\n");
+			ksft_inc_pass_cnt();
+		}
+
+
+		if (ret)
+			ksft_exit_fail();
+		else
+			ksft_exit_pass();
+	}
+
+	waitpid(pid2, &status, P_ALL);
+
+	return 0;
+}