On Sun, Nov 24, 2019 at 10:19:46PM +0000, Michael Kelley wrote: > From: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> Sent: Thursday, November 21, 2019 3:44 AM > > > > On Thu, Nov 21, 2019 at 12:50:17AM +0000, Dexuan Cui wrote: > > > > From: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> > > > > Sent: Wednesday, November 20, 2019 9:20 AM > > > > > > > > On Tue, Nov 19, 2019 at 11:16:56PM -0800, Dexuan Cui wrote: > > > > > Implement the suspend/resume callbacks. > > > > > > > > > > We must make sure there is no pending work items before we call > > > > > vmbus_close(). > > > > > > > > Where ? Why ? Imagine a developer reading this log to try to understand > > > > why you made this change, do you really think this commit log is > > > > informative in its current form ? > > > > > > > > I am not asking a book but this is a significant feature please make > > > > an effort to explain it (I can update the log for you but please > > > > write one and I shall do it). > > > > > > > > Lorenzo > > > > > > Sorry for being sloppy on this patch's changelog! Can you please use the > > > below? I can also post v3 with the new changelog if that's better. > > > > As you wish but more importantly get hyper-V maintainers to ACK these > > changes since time is running out for v5.5. > > > > Lorenzo > > > > > PCI: hv: Add the support of hibernation > > > > > > hv_pci_suspend() runs in a process context as a callback in dpm_suspend(). > > > When it starts to run, the channel callback hv_pci_onchannelcallback(), > > > which runs in a tasklet context, can be still running concurrently and > > > scheduling new work items onto hbus->wq in hv_pci_devices_present() and > > > hv_pci_eject_device(), and the work item handlers can access the vmbus > > > channel, which can be being closed by hv_pci_suspend(), e.g. the work item > > > handler pci_devices_present_work() -> new_pcichild_device() writes to > > > the vmbus channel. > > > > > > To eliminate the race, hv_pci_suspend() disables the channel callback > > > tasklet, sets hbus->state to hv_pcibus_removing, and re-enables the tasklet. > > > > > > This way, when hv_pci_suspend() proceeds, it knows that no new work item > > > can be scheduled, and then it flushes hbus->wq and safely closes the vmbus > > > channel. > > > > > > Thanks, > > > -- Dexuan > > FWIW, I'd like to see the above level of detail also as comments in the code > Itself so that whoever next looks at the code sees the explanation directly > without having to review the commit logs. > > Also, the commit message doesn't say what the commit actually does and > why. I'd suggest the commit message along these lines: > > Add suspend() and resume() functions so that Hyper-V virtual PCI devices are > handled properly when the VM hibernates and resumes from hibernation. > > Note that the suspend() function must make sure there are no pending work > items before calling vmbus_close(), since it runs in a process context as a > callback in dpm_suspend(). When it starts to run, the channel callback > hv_pci_onchannelcallback(), which runs in a tasklet context, can be still running > concurrently and scheduling new work items onto hbus->wq in > hv_pci_devices_present() and hv_pci_eject_device(), and the work item > handlers can access the vmbus channel, which can be being closed by > hv_pci_suspend(), e.g. the work item handler pci_devices_present_work() -> > new_pcichild_device() writes to the vmbus channel. > > To eliminate the race, hv_pci_suspend() disables the channel callback > tasklet, sets hbus->state to hv_pcibus_removing, and re-enables the tasklet. > This way, when hv_pci_suspend() proceeds, it knows that no new work item > can be scheduled, and then it flushes hbus->wq and safely closes the vmbus > channel. This is much better, thank you, if you are happy with the patches please add your tags so that I can pull the series asap, hopefully we can merge it in v5.5. Thanks, Lorenzo
