FAILED: patch "[PATCH] cxl/port: Fix delete_endpoint() vs parent unregistration race" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 8d2ad999ca3c64cb08cf6a58d227b9d9e746d708
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023112353-massive-tiara-8774@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

8d2ad999ca3c ("cxl/port: Fix delete_endpoint() vs parent unregistration race") 516b300c4ca8 ("cxl/memdev: Formalize endpoint port linkage") 0a105ab28a4d ("cxl/memdev: Warn of poison inject or clear to a mapped region") 9690b07748d1 ("cxl/memdev: Add support for the Clear Poison mailbox command") d2fbc4865802 ("cxl/memdev: Add support for the Inject Poison mailbox command") f0832a586396 ("cxl/region: Provide region info to the cxl_poison trace event") 7ff6ad107588 ("cxl/memdev: Add trigger_poison_list sysfs attribute") ed83f7ca398b ("cxl/mbox: Add GET_POISON_LIST mailbox command") d0abf5787adc ("cxl/mbox: Initialize the poison state") d35b495ddf92 ("cxl/port: Fix find_cxl_root() for RCDs and simplify it") 23c198e3dfaa ("Merge branch 'for-6.3/cxl-events' into cxl/next")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8d2ad999ca3c64cb08cf6a58d227b9d9e746d708 Mon Sep 17 00:00:00 2001
From: Dan Williams <[email protected]>
Date: Fri, 27 Oct 2023 20:13:23 -0700
Subject: [PATCH] cxl/port: Fix delete_endpoint() vs parent unregistration race

The CXL subsystem, at cxl_mem ->probe() time, establishes a lineage of ports (struct cxl_port objects) between an endpoint and the root of a CXL topology. Each port including the endpoint port is attached to the cxl_port driver.

Given that setup, it follows that when either any port in that lineage goes through a cxl_port ->remove() event, or the memdev goes through a cxl_mem ->remove() event. The hierarchy below the removed port, or the entire hierarchy if the memdev is removed needs to come down.

The delete_endpoint() callback is careful to check whether it is being called to tear down the hierarchy, or if it is only being called to teardown the memdev because an ancestor port is going through ->remove().

That care needs to take the device_lock() of the endpoint's parent. Which requires 2 bugs to be fixed:

1/ A reference on the parent is needed to prevent use-after-free
scenarios like this signature:

    BUG: spinlock bad magic on CPU#0, kworker/u56:0/11
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20230524-3.fc38 05/24/2023
    Workqueue: cxl_port detach_memdev [cxl_core]
    RIP: 0010:spin_bug+0x65/0xa0
    Call Trace:
      do_raw_spin_lock+0x69/0xa0
     __mutex_lock+0x695/0xb80
     delete_endpoint+0xad/0x150 [cxl_core]
     devres_release_all+0xb8/0x110
     device_unbind_cleanup+0xe/0x70
     device_release_driver_internal+0x1d2/0x210
     detach_memdev+0x15/0x20 [cxl_core]
     process_one_work+0x1e3/0x4c0
     worker_thread+0x1dd/0x3d0

2/ In the case of RCH topologies, the parent device that needs to be
locked is not always @port->dev as returned by cxl_mem_find_port(), use endpoint->dev.parent instead.

index 7ca01a834e18..0fe915ec2cc2 100644
@@ -1217,35 +1217,39 @@ static struct device *grandparent(struct device *dev)
 	return NULL;
 }
 
+static struct device *endpoint_host(struct cxl_port *endpoint)
+{
+	struct cxl_port *port = to_cxl_port(endpoint->dev.parent);
+
+	if (is_cxl_root(port))
+		return port->uport_dev;
+	return &port->dev;
+}
+
 static void delete_endpoint(void *data)
 {
 	struct cxl_memdev *cxlmd = data;
 	struct cxl_port *endpoint = cxlmd->endpoint;
-	struct cxl_port *parent_port;
-	struct device *parent;
-
-	parent_port = cxl_mem_find_port(cxlmd, NULL);
-	if (!parent_port)
-		goto out;
-	parent = &parent_port->dev;
+	struct device *host = endpoint_host(endpoint);
 
-	device_lock(parent);
-	if (parent->driver && !endpoint->dead) {
-		devm_release_action(parent, cxl_unlink_parent_dport, endpoint);
-		devm_release_action(parent, cxl_unlink_uport, endpoint);
-		devm_release_action(parent, unregister_port, endpoint);
+	device_lock(host);
+	if (host->driver && !endpoint->dead) {
+		devm_release_action(host, cxl_unlink_parent_dport, endpoint);
+		devm_release_action(host, cxl_unlink_uport, endpoint);
+		devm_release_action(host, unregister_port, endpoint);
 	}
 	cxlmd->endpoint = NULL;
-	device_unlock(parent);
-	put_device(parent);
-out:
+	device_unlock(host);
 	put_device(&endpoint->dev);
+	put_device(host);
 }
 
 int cxl_endpoint_autoremove(struct cxl_memdev *cxlmd, struct cxl_port *endpoint)
 {
+	struct device *host = endpoint_host(endpoint);
 	struct device *dev = &cxlmd->dev;
 
+	get_device(host);
 	get_device(&endpoint->dev);
 	cxlmd->endpoint = endpoint;
 	cxlmd->depth = endpoint->depth;