linux-kernel - [PATCH 1/6] drivers: base: devres: Allow to release group on device release

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Message-ID: <20250212200542.515493-2-lucas.demarchi@intel.com>
Date: Wed, 12 Feb 2025 12:05:37 -0800
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: linux-kernel@...r.kernel.org
Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>,
	dri-devel@...ts.freedesktop.org,
	Danilo Krummrich <dakr@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lucas De Marchi <lucas.demarchi@...el.com>
Subject: [PATCH 1/6] drivers: base: devres: Allow to release group on device release

When releasing a device, if the release action causes a group to be
released, a warning is emitted because it can't find the group. This
happens because devres_release_all() moves the entire list to a todo
list and also move the group markers. Considering r* normal resource
nodes and g1 a group resource node:

		    g1 -----------.
		    v		  v
	r1 -> r2 -> g1[0] -> r3-> g[1] -> r4

After devres_release_all(), dev->devres_head becomes empty and the todo
list it iterates on becomes:

			       g1
			       v
	r1 -> r2 -> r3-> r4 -> g1[0]

When a call to component_del() is made and takes down the aggregate
device, a warning like this happen:

	RIP: 0010:devres_release_group+0x362/0x530
	...
	Call Trace:
	 <TASK>
	 component_unbind+0x156/0x380
	 component_unbind_all+0x1d0/0x270
	 mei_component_master_unbind+0x28/0x80 [mei_hdcp]
	 take_down_aggregate_device+0xc1/0x160
	 component_del+0x1c6/0x3e0
	 intel_hdcp_component_fini+0xf1/0x170 [xe]
	 xe_display_fini+0x1e/0x40 [xe]

Because the devres group corresponding to the hdcp component cannot be
found. Just ignore this corner case: if the dev->devres_head is empty
and the caller is trying to remove a group, it's likely in the process
of device cleanup so just ignore it instead of warning.

Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
---

The check for just an empty devres_head seems simple and sufficient,
although the caller of devres_release_group() can still shoot its own
foot. I thought about a flag on dev to check it's being removed, but I
want to know others' opinions first.

 drivers/base/devres.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index 93e7779ef21e8..b955a2f9520bf 100644
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -687,6 +687,13 @@ int devres_release_group(struct device *dev, void *id)
 		spin_unlock_irqrestore(&dev->devres_lock, flags);

 		release_nodes(dev, &todo);
+	} else if (list_empty(&dev->devres_head)) {
+		/*
+		 * dev is probably dying via devres_release_all(): groups
+		 * have already been removed and are on the process of
+		 * being released - don't touch and don't warn.
+		 */
+		spin_unlock_irqrestore(&dev->devres_lock, flags);
 	} else {
 		WARN_ON(1);
 		spin_unlock_irqrestore(&dev->devres_lock, flags);
-- 
2.48.1