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

1 files changed, 66 insertions, 0 deletions

diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
new file mode 100644
index 000000000..c7524e4c5
--- /dev/null
+++ b/drivers/cpuidle/poll_state.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * poll_state.c - Polling idle state
+ */
+
+#include <linux/cpuidle.h>
+#include <linux/export.h>
+#include <linux/irqflags.h>
+#include <linux/sched.h>
+#include <linux/sched/clock.h>
+#include <linux/sched/idle.h>
+#include <linux/sprintf.h>
+#include <linux/types.h>
+
+#define POLL_IDLE_RELAX_COUNT	200
+
+static int __cpuidle poll_idle(struct cpuidle_device *dev,
+			       struct cpuidle_driver *drv, int index)
+{
+	u64 time_start;
+
+	time_start = local_clock_noinstr();
+
+	dev->poll_time_limit = false;
+
+	raw_local_irq_enable();
+	if (!current_set_polling_and_test()) {
+		unsigned int loop_count = 0;
+		u64 limit;
+
+		limit = cpuidle_poll_time(drv, dev);
+
+		while (!need_resched()) {
+			cpu_relax();
+			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
+				continue;
+
+			loop_count = 0;
+			if (local_clock_noinstr() - time_start > limit) {
+				dev->poll_time_limit = true;
+				break;
+			}
+		}
+	}
+	raw_local_irq_disable();
+
+	current_clr_polling();
+
+	return index;
+}
+
+void cpuidle_poll_state_init(struct cpuidle_driver *drv)
+{
+	struct cpuidle_state *state = &drv->states[0];
+
+	snprintf(state->name, CPUIDLE_NAME_LEN, "POLL");
+	snprintf(state->desc, CPUIDLE_DESC_LEN, "CPUIDLE CORE POLL IDLE");
+	state->exit_latency = 0;
+	state->target_residency = 0;
+	state->exit_latency_ns = 0;
+	state->target_residency_ns = 0;
+	state->power_usage = -1;
+	state->enter = poll_idle;
+	state->flags = CPUIDLE_FLAG_POLLING;
+}
+EXPORT_SYMBOL_GPL(cpuidle_poll_state_init);