> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] > Sent: Wednesday, June 1, 2016 0:27 > To: Dexuan Cui <decui@xxxxxxxxxxxxx> > Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; driverdev- > devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; > jasowang@xxxxxxxxxx; KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang > Zhang <haiyangz@xxxxxxxxxxxxx>; rolf.neugebauer@xxxxxxxxxx; > dave.scott@xxxxxxxxxx; ian.campbell@xxxxxxxxxx > Subject: Re: [PATCH v3] Drivers: hv: vmbus: fix the race when querying & > updating the percpu list > > Dexuan Cui <decui@xxxxxxxxxxxxx> writes: > > > There is a rare race when we remove an entry from the global list > > hv_context.percpu_list[cpu] in hv_process_channel_removal() -> > > percpu_channel_deq() -> list_del(): at this time, if vmbus_on_event() -> > > process_chn_event() -> pcpu_relid2channel() is trying to query the list, > > we can get the kernel fault. > > > > Similarly, we also have the issue in the code path: vmbus_process_offer() > -> > > percpu_channel_enq(). > > > > We can resolve the issue by disabling the tasklet when updating the list. > > > > The patch also moves vmbus_release_relid() to a later place where > > the channel has been removed from the per-cpu and the global lists. > > > > Reported-by: Rolf Neugebauer <rolf.neugebauer@xxxxxxxxxx> > > Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > > Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> > > Tested 4.7-rc1 with this path applied and kernel always crashes on boot > (WS2016TP5, 12 CPU SMP guest, Generation 2): > > [ 5.464251] hv_vmbus: Hyper-V Host Build:14300-10.0-1-0.1006; Vmbus > version:4.0 > [ 5.471666] hv_vmbus: Unknown GUID: f8e65716-3cb3-4a06-9a60- > 1889c5cccab5 > [ 5.472143] BUG: unable to handle kernel paging request at > 000000079fff5288 > [ 5.477107] IP: [<ffffffffa0004b91>] vmbus_onoffer+0x311/0x570 > [hv_vmbus] > ... > Vitaly I can't reproduce the panic somehow, but I did find a bug in vmbus_process_offer(): "hv_event_tasklet_disable(channel) and hv_event_tasklet_enable(channel)" are buggy: the 'channel' parameter should be 'newchannel'. This was a copy-and-paste bug... Sorry! Can you fix this and see if the panic will disappear in your side? Thanks, -- Dexuan _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
