RE: [PATCH v4 1/2] PCI: hv: Serialize the present and eject work items

[Dexuan Cui]

> From: Dexuan Cui
> > From: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> > I need to know either what commit you are fixing (ie Fixes: tag - which
> > is preferrable) or you tell me which kernel versions we are targeting
> > for the stable backport.
> > Lorenzo
> 
> Sorry.  Here I was hesitant to add a "Fixes:" because the bug was there the first
> day
> when the driver was introduced.
> 
> Please use
> Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft
> Hyper-V VMs")
> or
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.6+

BTW, the bug here is a race condtion which couldn't be easily hit in the past,
probably because most of the time only one PCI device was only added into the
VM once. But now it's becoming typical that a VM can have 4 GPU devices so we
start to notice this bug. With 7 Mellanox VFs assigned to a VM, we can easily
reproduce the bug by "hot-remove and hot-add VFs" test:

general protection fault: 0000 [#1] SMP
...
Workqueue: events hv_eject_device_work [pci_hyperv]
task: ffff8800ed5e5400 ti: ffff8800ee674000 task.ti: ffff8800ee674000
RIP: 0010:[<ffffffffc025c5ce>]  ... hv_eject_device_work+0xbe/0x160 [pci_hyperv]
...
Call Trace:
 [<ffffffff8183c3a6>] ? __schedule+0x3b6/0xa30
 [<ffffffff8109a585>] process_one_work+0x165/0x480
 [<ffffffff8109a8eb>] worker_thread+0x4b/0x4c0
 [<ffffffff8109a8a0>] ? process_one_work+0x480/0x480
 [<ffffffff810a0c25>] kthread+0xe5/0x100
 [<ffffffff810a0b40>] ? kthread_create_on_node+0x1e0/0x1e0
 [<ffffffff81840f0f>] ret_from_fork+0x3f/0x70
 [<ffffffff810a0b40>] ? kthread_create_on_node+0x1e0/0x1e0
Code: ...
RIP  [<ffffffffc025c5ce>] hv_eject_device_work+0xbe/0x160 [pci_hyperv]
...
BUG: unable to handle kernel paging request at ffffffffffffffd8
IP: [<ffffffff810a12d0>] kthread_data+0x10/0x20
PGD 1e0d067 PUD 1e0f067 PMD 0
Oops: 0000 [#2] SMP
 
Thanks,
-- Dexuan