6.6-stable review patch. If anyone has any objections, please let me know.
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From: John Ernberg john.ernberg@actia.se
commit 0d9cfc9b8cb17dbc29a98792d36ec39a1cf1395f upstream.
The Gemalto Cinterion PLS83-W modem (cdc_ether) is emitting confusing link up and down events when the WWAN interface is activated on the modem-side.
Interrupt URBs will in consecutive polls grab: * Link Connected * Link Disconnected * Link Connected
Where the last Connected is then a stable link state.
When the system is under load this may cause the unlink_urbs() work in __handle_link_change() to not complete before the next usbnet_link_change() call turns the carrier on again, allowing rx_submit() to queue new SKBs.
In that event the URB queue is filled faster than it can drain, ending up in a RCU stall:
rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-.... } 33108 jiffies s: 201 root: 0x1/. rcu: blocking rcu_node structures (internal RCU debug): Sending NMI from CPU 1 to CPUs 0: NMI backtrace for cpu 0
Call trace: arch_local_irq_enable+0x4/0x8 local_bh_enable+0x18/0x20 __netdev_alloc_skb+0x18c/0x1cc rx_submit+0x68/0x1f8 [usbnet] rx_alloc_submit+0x4c/0x74 [usbnet] usbnet_bh+0x1d8/0x218 [usbnet] usbnet_bh_tasklet+0x10/0x18 [usbnet] tasklet_action_common+0xa8/0x110 tasklet_action+0x2c/0x34 handle_softirqs+0x2cc/0x3a0 __do_softirq+0x10/0x18 ____do_softirq+0xc/0x14 call_on_irq_stack+0x24/0x34 do_softirq_own_stack+0x18/0x20 __irq_exit_rcu+0xa8/0xb8 irq_exit_rcu+0xc/0x30 el1_interrupt+0x34/0x48 el1h_64_irq_handler+0x14/0x1c el1h_64_irq+0x68/0x6c _raw_spin_unlock_irqrestore+0x38/0x48 xhci_urb_dequeue+0x1ac/0x45c [xhci_hcd] unlink1+0xd4/0xdc [usbcore] usb_hcd_unlink_urb+0x70/0xb0 [usbcore] usb_unlink_urb+0x24/0x44 [usbcore] unlink_urbs.constprop.0.isra.0+0x64/0xa8 [usbnet] __handle_link_change+0x34/0x70 [usbnet] usbnet_deferred_kevent+0x1c0/0x320 [usbnet] process_scheduled_works+0x2d0/0x48c worker_thread+0x150/0x1dc kthread+0xd8/0xe8 ret_from_fork+0x10/0x20
Get around the problem by delaying the carrier on to the scheduled work.
This needs a new flag to keep track of the necessary action.
The carrier ok check cannot be removed as it remains required for the LINK_RESET event flow.
Fixes: 4b49f58fff00 ("usbnet: handle link change") Cc: stable@vger.kernel.org Signed-off-by: John Ernberg john.ernberg@actia.se Link: https://patch.msgid.link/20250723102526.1305339-1-john.ernberg@actia.se Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/usb/usbnet.c | 11 ++++++++--- include/linux/usb/usbnet.h | 1 + 2 files changed, 9 insertions(+), 3 deletions(-)
--- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -1122,6 +1122,9 @@ static void __handle_link_change(struct * tx queue is stopped by netcore after link becomes off */ } else { + if (test_and_clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags)) + netif_carrier_on(dev->net); + /* submitting URBs for reading packets */ tasklet_schedule(&dev->bh); } @@ -2015,10 +2018,12 @@ EXPORT_SYMBOL(usbnet_manage_power); void usbnet_link_change(struct usbnet *dev, bool link, bool need_reset) { /* update link after link is reseted */ - if (link && !need_reset) - netif_carrier_on(dev->net); - else + if (link && !need_reset) { + set_bit(EVENT_LINK_CARRIER_ON, &dev->flags); + } else { + clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags); netif_carrier_off(dev->net); + }
if (need_reset && link) usbnet_defer_kevent(dev, EVENT_LINK_RESET); --- a/include/linux/usb/usbnet.h +++ b/include/linux/usb/usbnet.h @@ -76,6 +76,7 @@ struct usbnet { # define EVENT_LINK_CHANGE 11 # define EVENT_SET_RX_MODE 12 # define EVENT_NO_IP_ALIGN 13 +# define EVENT_LINK_CARRIER_ON 14 /* This one is special, as it indicates that the device is going away * there are cyclic dependencies between tasklet, timer and bh * that must be broken