PCI: endpoint: pci-epf-vntb: Stop cmd_handler work in epf_ntb_epc_cleanup

In the Linux kernel, the following vulnerability has been resolved:

PCI: endpoint: pci-epf-vntb: Stop cmd_handler work in epf_ntb_epc_cleanup

Disable the delayed work before clearing BAR mappings and doorbells to

avoid running the handler after resources have been torn down.

Unable to handle kernel paging request at virtual address ffff800083f46004

[...]

Internal error: Oops: 0000000096000007 [#1] SMP

[...]

Call trace:

epf_ntb_cmd_handler+0x54/0x200 [pci_epf_vntb] (P)

process_one_work+0x154/0x3b0

worker_thread+0x2c8/0x400

kthread+0x148/0x210

ret_from_fork+0x10/0x20