linux-kernel - [PATCH] Bluetooth: Fix suspend notifier race

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Message-Id: <20200727142231.1.I7ebe9eaf684ddb07ae28634cb4d28cf7754641f1@changeid>
Date:   Mon, 27 Jul 2020 14:22:47 -0700
From:   Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
To:     marcel@...tmann.org
Cc:     chromeos-bluetooth-upstreaming@...omium.org,
        linux-bluetooth@...r.kernel.org,
        Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
        Miao-chen Chou <mcchou@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Johan Hedberg <johan.hedberg@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH] Bluetooth: Fix suspend notifier race

Unregister from suspend notifications and cancel suspend preparations
before running hci_dev_do_close. Otherwise, the suspend notifier may
race with unregister and cause cmd_timeout even after hdev has been
freed.

Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
Reviewed-by: Miao-chen Chou <mcchou@...omium.org>
---
Hi Marcel,

This fixes a race between hci_unregister_dev and the suspend notifier.
Without these changes, we encountered the following kernel panic when
a USB disconnect (with btusb) occurred on resume:

[  832.578518] Bluetooth: hci_core.c:hci_cmd_timeout() hci0: command 0x0c05 tx timeout
[  832.586200] BUG: kernel NULL pointer dereference, address: 0000000000000000
[  832.586203] #PF: supervisor read access in kernel mode
[  832.586205] #PF: error_code(0x0000) - not-present page
[  832.586206] PGD 0 P4D 0
[  832.586210] PM: suspend exit
[  832.608870] Oops: 0000 [#1] PREEMPT SMP NOPTI
[  832.613232] CPU: 3 PID: 10755 Comm: kworker/3:7 Not tainted 5.4.44-04894-g1e9dbb96a161 #1
[  832.630036] Workqueue: events hci_cmd_timeout [bluetooth]
[  832.630046] RIP: 0010:__queue_work+0xf0/0x374
[  832.630051] RSP: 0018:ffff9b5285f1fdf8 EFLAGS: 00010046
[  832.674033] RAX: ffff8a97681bac00 RBX: 0000000000000000 RCX: ffff8a976a000600
[  832.681162] RDX: 0000000000000000 RSI: 0000000000000009 RDI: ffff8a976a000748
[  832.688289] RBP: ffff9b5285f1fe38 R08: 0000000000000000 R09: ffff8a97681bac00
[  832.695418] R10: 0000000000000002 R11: ffff8a976a0006d8 R12: ffff8a9745107600
[  832.698045] usb 1-6: new full-speed USB device number 119 using xhci_hcd
[  832.702547] R13: ffff8a9673658850 R14: 0000000000000040 R15: 000000000000001e
[  832.702549] FS:  0000000000000000(0000) GS:ffff8a976af80000(0000) knlGS:0000000000000000
[  832.702550] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  832.702550] CR2: 0000000000000000 CR3: 000000010415a000 CR4: 00000000003406e0
[  832.702551] Call Trace:
[  832.702558]  queue_work_on+0x3f/0x68
[  832.702562]  process_one_work+0x1db/0x396
[  832.747397]  worker_thread+0x216/0x375
[  832.751147]  kthread+0x138/0x140
[  832.754377]  ? pr_cont_work+0x58/0x58
[  832.758037]  ? kthread_blkcg+0x2e/0x2e
[  832.761787]  ret_from_fork+0x22/0x40
[  832.846191] ---[ end trace fa93f466da517212 ]---

The suspend notifier handler seemed to be scheduling commands even after
it was cleaned up and this was resulting in a panic in cmd_timeout (when
it tries to requeue the cmd_timer).

This was tested on 5.4 kernel with a suspend+resume stress test for 500+
iterations. I also confirmed that after a usb disconnect, the suspend
notifier times out before the USB device is probed again (fixing the
original race between the usb_disconnect + probe and the notifier).

Thanks
Abhishek


 net/bluetooth/hci_core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 6509f785dd1481..97221d1fa883d1 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -3765,9 +3765,10 @@ void hci_unregister_dev(struct hci_dev *hdev)
 
 	cancel_work_sync(&hdev->power_on);
 
-	hci_dev_do_close(hdev);
-
 	unregister_pm_notifier(&hdev->suspend_notifier);
+	cancel_work_sync(&hdev->suspend_prepare);
+
+	hci_dev_do_close(hdev);
 
 	if (!test_bit(HCI_INIT, &hdev->flags) &&
 	    !hci_dev_test_flag(hdev, HCI_SETUP) &&
-- 
2.28.0.rc0.142.g3c755180ce-goog