rpmsg: glink: fix deadlock in endpoint destroy during driver detach

During driver detach, the device core holds the device mutex throughout
the driver's remove callback chain.  When the rpmsg endpoint is
destroyed as part of that teardown, the GLINK endpoint destroy
implementation attempts to unregister the underlying rpmsg device.
That unregistration calls device_del(), which tries to re-acquire the
same device mutex already held higher up the stack, causing rmmod to
hang indefinitely.

The deadlock manifests with the following call chain:

[<0>] device_del+0x44/0x414  <- tries to acquire same mutex
[<0>] device_unregister+0x18/0x34
[<0>] rpmsg_unregister_device+0x28/0x4c
[<0>] qcom_glink_remove_rpmsg_device+0x70/0xc0
[<0>] qcom_glink_destroy_ept+0x58/0xbc
[<0>] rpmsg_dev_remove+0x50/0x60
[<0>] device_remove+0x4c/0x80
[<0>] device_release_driver_internal+0x1cc/0x228  <- acquires device mutex
[<0>] driver_detach+0x4c/0x98
[<0>] bus_remove_driver+0x6c/0xbc
[<0>] driver_unregister+0x30/0x60
[<0>] unregister_rpmsg_driver+0x10/0x1c
[<0>] fastrpc_exit+0x28/0x38 [fastrpc]
[<0>] __arm64_sys_delete_module+0x1b8/0x294
[<0>] invoke_syscall+0x48/0x10c
[<0>] el0_svc_common.constprop.0+0xc0/0xe0
[<0>] do_el0_svc+0x1c/0x28
[<0>] el0_svc+0x34/0x108
[<0>] el0t_64_sync_handler+0xa0/0xe4
[<0>] el0t_64_sync+0x198/0x19c

The rpmsg device unregistration inside endpoint destroy is redundant.
In both contexts where endpoint destruction is triggered:

- Driver detach path: the driver core already tears down the rpmsg
  device.

- Channel close path: the rpmsg device is already unregistered before
  endpoint destruction is reached.

Remove the redundant unregistration to fix the deadlock.

Co-developed-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
Signed-off-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
Tested-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
Fixes: a53e356df548 ("rpmsg: glink: fix rpmsg device leak")
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260604-rpmsg-glink-fix-deadlock-destroy-ept-v1-1-b8a54ad1e4fd@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

1 files changed, 0 insertions, 3 deletions

diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
index 022b4bcb40d6..55793fc18293 100644
--- a/drivers/rpmsg/qcom_glink_native.c
+++ b/drivers/rpmsg/qcom_glink_native.c
@@ -1418,9 +1418,6 @@ static void qcom_glink_destroy_ept(struct rpmsg_endpoint *ept)
 	channel->ept.cb = NULL;
 	spin_unlock_irqrestore(&channel->recv_lock, flags);
 
-	/* Decouple the potential rpdev from the channel */
-	qcom_glink_remove_rpmsg_device(glink, channel);
-
 	qcom_glink_send_close_req(glink, channel);
 }