linux-kernel - [RFC] driver core: Fix repeated device_is

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Date:   Tue,  5 Jul 2022 16:45:02 +0300
From:   Abel Vesa <abel.vesa@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Saravana Kannan <saravanak@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org, Abel Vesa <abel.vesa@...aro.org>
Subject: [RFC] driver core: Fix repeated device_is_dependent check for same link

In case of a cyclic dependency, if the supplier is not yet available,
the parent of the supplier is checked for dependency. But if there are
more than one suppliers with the same parent, the first check returns
true while the next checks skip that specific link entirely. So add a
flag that marks the link for future checks and bail early if it is
already marked with that flag.

Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
---

For more details about this issue, have a look at this thread:
https://lore.kernel.org/all/CAGETcx8F0wP+RA0KpjOJeZfc=DVG-MbM_=SkRHD4UhD2ReL7Kw@mail.gmail.com/

 drivers/base/core.c    | 14 +++++++++++---
 include/linux/device.h |  2 ++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index ccdd5b4295de..38cb478ae400 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -297,12 +297,18 @@ int device_is_dependent(struct device *dev, void *target)
 		return ret;

 	list_for_each_entry(link, &dev->links.consumers, s_node) {
+		/* if already marked before as dependent, bail early */
+		if (link->flags & DL_FLAG_DEVICE_IS_DEPENDENT)
+			return 1;
+
 		if ((link->flags & ~DL_FLAG_INFERRED) ==
 		    (DL_FLAG_SYNC_STATE_ONLY | DL_FLAG_MANAGED))
 			continue;

-		if (link->consumer == target)
+		if (link->consumer == target) {
+			link->flags |= DL_FLAG_DEVICE_IS_DEPENDENT;
 			return 1;
+		}

 		ret = device_is_dependent(link->consumer, target);
 		if (ret)
@@ -1660,11 +1666,13 @@ static void fw_devlink_relax_link(struct device_link *link)
 	if (!(link->flags & DL_FLAG_INFERRED))
 		return;

-	if (link->flags == (DL_FLAG_MANAGED | FW_DEVLINK_FLAGS_PERMISSIVE))
+	if ((link->flags & (DL_FLAG_MANAGED | FW_DEVLINK_FLAGS_PERMISSIVE)) ==
+			(DL_FLAG_MANAGED | FW_DEVLINK_FLAGS_PERMISSIVE))
 		return;

 	pm_runtime_drop_link(link);
-	link->flags = DL_FLAG_MANAGED | FW_DEVLINK_FLAGS_PERMISSIVE;
+	link->flags &= DL_FLAG_DEVICE_IS_DEPENDENT;
+	link->flags |= DL_FLAG_MANAGED | FW_DEVLINK_FLAGS_PERMISSIVE;
 	dev_dbg(link->consumer, "Relaxing link with %s\n",
 		dev_name(link->supplier));
 }
diff --git a/include/linux/device.h b/include/linux/device.h
index 424b55df0272..3b0c4b777a60 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -317,6 +317,7 @@ enum device_link_state {
  * MANAGED: The core tracks presence of supplier/consumer drivers (internal).
  * SYNC_STATE_ONLY: Link only affects sync_state() behavior.
  * INFERRED: Inferred from data (eg: firmware) and not from driver actions.
+ * DEVICE_IS_DEPENDENT: The consumer is dependent on the supplier
  */
 #define DL_FLAG_STATELESS		BIT(0)
 #define DL_FLAG_AUTOREMOVE_CONSUMER	BIT(1)
@@ -327,6 +328,7 @@ enum device_link_state {
 #define DL_FLAG_MANAGED			BIT(6)
 #define DL_FLAG_SYNC_STATE_ONLY		BIT(7)
 #define DL_FLAG_INFERRED		BIT(8)
+#define DL_FLAG_DEVICE_IS_DEPENDENT	BIT(9)

 /**
  * enum dl_dev_state - Device driver presence tracking information.
--
2.34.3