commit 0d9cfc9b8c 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: 4b49f58fff ("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>
e2a4325ce2