> -----Original Message----- > From: mika.westerberg@xxxxxxxxxxxxxxx > [mailto:mika.westerberg@xxxxxxxxxxxxxxx] > Sent: 13 November 2018 15:08 > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx> > Cc: linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Wangzhou (B) > <wangzhou1@xxxxxxxxxxxxx>; Linuxarm <linuxarm@xxxxxxxxxx>; Lukas > Wunner <lukas@xxxxxxxxx> > Subject: Re: Qemu Guest kernel 4.20-rc1 PCIe hotplug issue [...] > > Right. As I mentioned in my previous mail, I missed the fact that you are > updating > > the ctrl->slot_ctrl with cmd value while in my test I did my update with the > value > > returned by pcie_capability_read_word(). > > OK, I see. > > > > However, I think we are missing check for PCI_EXP_SLTCTL_CCIE in > > > pciehp_isr(). > > > > Ok. > > > > > Here's an updated patch, can you try and see if it makes any difference? > > > > I just tried this and it works. Thanks. > > Can you still check that the previous one (without _CCIE check) works? Yes, it works for me without _CCIE. > > See few comments below. > > > > > diff --git a/drivers/pci/hotplug/pciehp_hpc.c > > > b/drivers/pci/hotplug/pciehp_hpc.c > > > index 7dd443aea5a5..da2cbe892444 100644 > > > --- a/drivers/pci/hotplug/pciehp_hpc.c > > > +++ b/drivers/pci/hotplug/pciehp_hpc.c > > > @@ -156,9 +156,9 @@ static void pcie_do_write_cmd(struct controller > *ctrl, > > > u16 cmd, > > > slot_ctrl |= (cmd & mask); > > > ctrl->cmd_busy = 1; > > > smp_mb(); > > > + ctrl->slot_ctrl = slot_ctrl; > > > > Does it make more sense if we can move this before smp_mb()?. Also I am > not > > sure updating the ctrl->slot_ctrl before actually the hardware is > programmed > > with that value will result in any other race conditions? TBH, I am not that > familiar > > with this code and I leave that to you :) > > Both are good questions :) > > For the moving ctrl->slot_ctrl before pcie_capability_write_word(), I > think we should be fine and this is actually more correct because if we > are unmasking interrupts they may trigger immediately making > pciehp_isr() find wrong values in ctrl->slot_ctrl (as can be seen in the > issue you reported). Ok. I was more concerned about an unsolicited event triggering the _isr while we are modifying the ctrl->slot_ctrl. But that's ok I think as the _isr reads the hw status anyway. > The smb_mb() thing is not that clear (at least to me) because it is used > in two places in the driver and both seem to be making write to > ctrl->cmd_busy visible to other CPUs but I don't see where we deal with > the read part. > > I may be missing something, though. I think the read part is in wait_event_timeout() which evaluates the condition. The wake_up is called from the pciehp_isr(). Since the flag is being updated in both process level and interrupt handler context, smp_mb() is used. I think the same now applies to ctrl->slot_ctrl now as this being used in process context and interrupt context as well. Thanks, Shameer
