This is a note to let you know that I've just added the patch titled
cxl/port: Fix delete_endpoint() vs parent unregistration race
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cxl-port-fix-delete_endpoint-vs-parent-unregistratio.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1fb8159e9c2490c44b8cf3061ec4b7598ed0cb7d
Author: Dan Williams <dan.j.williams@xxxxxxxxx>
Date: Fri Oct 27 20:13:23 2023 -0700
cxl/port: Fix delete_endpoint() vs parent unregistration race
[ Upstream commit 8d2ad999ca3c64cb08cf6a58d227b9d9e746d708 ]
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.
Fixes: 8dd2bc0f8e02 ("cxl/mem: Add the cxl_mem driver")
Cc: <stable@xxxxxxxxxxxxxxx>
Reported-by: Robert Richter <rrichter@xxxxxxx>
Closes: http://lore.kernel.org/r/20231018171713.1883517-2-rrichter@xxxxxxx
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index 2c6001592fe20..6a75a3cb601ec 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -1242,35 +1242,39 @@ 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;
