linux-kernel - [RFC v2] driver core: Fix repeated device_is

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Date:   Wed,  6 Jul 2022 18:53:47 +0300
From:   Abel Vesa <abel.vesa@...aro.org>
To:     Saravana Kannan <saravanak@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     linux-arm-msm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Abel Vesa <abel.vesa@...aro.org>
Subject: [RFC v2] 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 ones skip that specific link entirely because of
having DL_FLAG_MANAGED and DL_FLAG_SYNC_STATE_ONLY set, which is what
the relaxing of the link does. But if we check for the target being
a consumer before the check for those flags, we can check as many
times as needed the same link and it will always return true, This is
safe to do, since the relaxing of the link will be done only once
because those flags will be set and it will bail early.

Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
---
 drivers/base/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 753e7cca0f40..2c3b860dfe80 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -297,13 +297,13 @@ int device_is_dependent(struct device *dev, void *target)
 		return ret;

 	list_for_each_entry(link, &dev->links.consumers, s_node) {
+		if (link->consumer == target)
+			return 1;
+
 		if ((link->flags & ~DL_FLAG_INFERRED) ==
 		    (DL_FLAG_SYNC_STATE_ONLY | DL_FLAG_MANAGED))
 			continue;

-		if (link->consumer == target)
-			return 1;
-
 		ret = device_is_dependent(link->consumer, target);
 		if (ret)
 			break;
--
2.34.3