Patch "Bluetooth: hci_serdev: Init hci_uart proto_lock to avoid oops" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

Bluetooth: hci_serdev: Init hci_uart proto_lock to avoid oops

to the 4.15-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:
bluetooth-hci_serdev-init-hci_uart-proto_lock-to-avoid-oops.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lukas Wunner <[email protected]>
Date: Fri, 17 Nov 2017 00:54:53 +0100
Subject: Bluetooth: hci_serdev: Init hci_uart proto_lock to avoid oops
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From: Lukas Wunner <[email protected]>

commit d73e172816652772114827abaa2dbc053eecbbd7 upstream.

John Stultz reports a boot time crash with the HiKey board (which uses hci_serdev) occurring in hci_uart_tx_wakeup(). That function is contained in hci_ldisc.c, but also called from the newer hci_serdev.c. It acquires the proto_lock in struct hci_uart and it turns out that we forgot to init the lock in the serdev code path, thus causing the crash.

John bisected the crash to commit 67d2f8781b9f ("Bluetooth: hci_ldisc:
Allow sleeping while proto locks are held"), but the issue was present before and the commit merely exposed it. (Perhaps by luck, the crash did not occur with rwlocks.)

Init the proto_lock in the serdev code path to avoid the oops.

Stack trace for posterity:

Unable to handle kernel read from unreadable memory at 406f127000
[000000406f127000] user address but active_mm is swapper
Internal error: Oops: 96000005 [#1] PREEMPT SMP
Hardware name: HiKey Development Board (DT)
Call trace:
 hci_uart_tx_wakeup+0x38/0x148
 hci_uart_send_frame+0x28/0x38
 hci_send_frame+0x64/0xc0
 hci_cmd_work+0x98/0x110
 process_one_work+0x134/0x330
 worker_thread+0x130/0x468
 kthread+0xf8/0x128
 ret_from_fork+0x10/0x18

---
 drivers/bluetooth/hci_serdev.c |    1 +
 1 file changed, 1 insertion(+)

@@ -303,6 +303,7 @@ int hci_uart_register_device(struct hci_
 	hci_set_drvdata(hdev, hu);
 
 	INIT_WORK(&hu->write_work, hci_uart_write_work);
+	percpu_init_rwsem(&hu->proto_lock);
 
 	/* Only when vendor specific setup callback is provided, consider
 	 * the manufacturer information valid. This avoids filling in the

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/bluetooth-hci_serdev-init-hci_uart-proto_lock-to-avoid-oops.patch