Re: [PATCH v2] PCI/LINK: bw_notification: Do not leave interrupt handler NULL

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 19 Apr 2019 15:08:27 -0600
Alex Williamson <alex.williamson@redhat.com> wrote:

> On Mon, 25 Mar 2019 17:25:02 -0500
> Bjorn Helgaas <helgaas@kernel.org> wrote:
> 
> > On Fri, Mar 22, 2019 at 07:36:51PM -0500, Alexandru Gagniuc wrote:  
> > > A threaded IRQ with a NULL handler does not work with level-triggered
> > > interrupts. request_threaded_irq() will return an error:
> > > 
> > >   genirq: Threaded irq requested with handler=NULL and !ONESHOT for irq 16
> > >   pcie_bw_notification: probe of 0000:00:1b.0:pcie010 failed with error -22
> > > 
> > > For level interrupts we need to silence the interrupt before exiting
> > > the IRQ handler, so just clear the PCI_EXP_LNKSTA_LBMS bit there.
> > > 
> > > Fixes: e8303bb7a75c ("PCI/LINK: Report degraded links via link bandwidth notification")
> > > Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> > > Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>    
> > 
> > Applied with the following subject line to for-linus for v5.1, thanks!
> > 
> >   PCI/LINK: Supply IRQ handler so level-triggered IRQs are acked  
> 
> That made it a little tricky to track down this thread.  I get a
> regression bisected back to this when trying to do vfio device
> assignment.  I haven't dug further than the bisection, but I assume bus
> resets are triggering this link bandwidth notifier code and nobody
> thinks it's their interrupt:

I'm not sure what to do with this, I think it bisects back to commit
3e82a7f9031f simply because the interrupt was failing to register prior
to that, so the bandwidth notifier code was never activated (how was
this tested?).  When I assign a GPU to a VM, the VM is manipulating the
device to change the link speed, I would have thought this would
trigger the autonomous bandwidth notification, but I can clearly see
BWMgmt+ ABWMgmt- in lspci.  The root port shows:

  Interrupt: pin A routed to IRQ 25

And the BW notifier interrupt is registered here:

25: 0 ... 0 IR-IO-APIC    8-fasteoi   PCIe BW notif

There's no interrupt count for any CPU on this vector.  For all I know,
this IRQ routing has never been exercised and could be broken in the
BIOS, resulting in the a random spurious IRQ victim.  There seems to be
no good way to disable this driver other than manually unbinding root
ports via sysfs.  That's not a great solution.  The system is an Intel
X79 based workstation.  Suggestions for further debugging? Thanks,

Alex

> [  119.910738] irq 16: nobody cared (try booting with the "irqpoll" option)
> [  119.917455] CPU: 18 PID: 0 Comm: swapper/18 Not tainted 5.1.0-rc1+ #29
> [  119.923998] Hardware name: Hewlett-Packard HP Z820 Workstation/158B, BIOS J63 v03.69 03/25/2014
> [  119.932715] Call Trace:
> [  119.935169]  <IRQ>
> [  119.937200]  dump_stack+0x46/0x60
> [  119.940534]  __report_bad_irq+0x37/0xae
> [  119.944380]  note_interrupt.cold.9+0xa/0x69
> [  119.948580]  handle_irq_event_percpu+0x6a/0x80
> [  119.953037]  handle_irq_event+0x3d/0x5a
> [  119.956887]  handle_fasteoi_irq+0x8b/0x140
> [  119.961003]  handle_irq+0xbf/0x100
> [  119.964420]  do_IRQ+0x49/0xd0
> [  119.967398]  common_interrupt+0xf/0xf
> [  119.971074]  </IRQ>
> [  119.973190] RIP: 0010:cpuidle_enter_state+0xb4/0x460
> [  119.978167] Code: 24 0f 1f 44 00 00 31 ff e8 69 bf a3 ff 80 7c 24 13 00 74 12 9c 58 f6 c4 02 0f 85 7d 03 00 00 31 ff e8 60 cf a9 ff fb 45 85 e4 <0f> 88 ae 02 00 00 49 63 cc 4c 8b 3c 24 4c 2b 7c 24 08 48 8d 04 49
> [  119.996967] RSP: 0018:ffffb6740330fe98 EFLAGS: 00000202 ORIG_RAX: ffffffffffffffda
> [  120.004549] RAX: ffff9dbfc19a1d80 RBX: ffffffff82d2c940 RCX: 000000000000001f
> [  120.011700] RDX: 0000001beb3c9b05 RSI: 00000000315975dc RDI: 0000000000000000
> [  120.018845] RBP: ffff9dbfc19acc00 R08: 0000000000000002 R09: 0000000000021640
> [  120.025990] R10: 0000027ae2689456 R11: ffff9dbfc19a0e64 R12: 0000000000000004
> [  120.033146] R13: ffffffff82d2cad8 R14: 0000000000000004 R15: 0000000000000000
> [  120.040303]  ? cpuidle_enter_state+0x97/0x460
> [  120.044679]  do_idle+0x1f1/0x230
> [  120.047918]  cpu_startup_entry+0x19/0x20
> [  120.051856]  start_secondary+0x172/0x1c0
> [  120.055796]  secondary_startup_64+0xb6/0xc0
> [  120.059993] handlers:
> [  120.062283] [<0000000054c59383>] usb_hcd_irq
> [  120.066563] Disabling IRQ #16
> [  122.885627] irq 16: nobody cared (try booting with the "irqpoll" option)
> [  122.892326] CPU: 18 PID: 0 Comm: swapper/18 Not tainted 5.1.0-rc1+ #29
> [  122.898847] Hardware name: Hewlett-Packard HP Z820 Workstation/158B, BIOS J63 v03.69 03/25/2014
> [  122.907532] Call Trace:
> [  122.909985]  <IRQ>
> [  122.912009]  dump_stack+0x46/0x60
> [  122.915325]  __report_bad_irq+0x37/0xae
> [  122.919159]  note_interrupt.cold.9+0xa/0x69
> [  122.923338]  handle_irq_event_percpu+0x6a/0x80
> [  122.927781]  handle_irq_event+0x3d/0x5a
> [  122.931630]  handle_fasteoi_irq+0x8b/0x140
> [  122.935730]  handle_irq+0xbf/0x100
> [  122.939137]  do_IRQ+0x49/0xd0
> [  122.942108]  common_interrupt+0xf/0xf
> [  122.945772]  </IRQ>
> [  122.947881] RIP: 0010:cpuidle_enter_state+0xb4/0x460
> [  122.952845] Code: 24 0f 1f 44 00 00 31 ff e8 69 bf a3 ff 80 7c 24 13 00 74 12 9c 58 f6 c4 02 0f 85 7d 03 00 00 31 ff e8 60 cf a9 ff fb 45 85 e4 <0f> 88 ae 02 00 00 49 63 cc 4c 8b 3c 24 4c 2b 7c 24 08 48 8d 04 49
> [  122.971629] RSP: 0018:ffffb6740330fe98 EFLAGS: 00000202 ORIG_RAX: ffffffffffffffda
> [  122.979212] RAX: ffff9dbfc19a1d80 RBX: ffffffff82d2c940 RCX: 000000000000001f
> [  122.986361] RDX: 0000001c9c8daa6e RSI: 00000000315975dc RDI: 0000000000000000
> [  122.993517] RBP: ffff9dbfc19acc00 R08: 0000000000000002 R09: 0000000000021640
> [  123.000655] R10: 0000027cae52b176 R11: ffff9dbfc19a0e64 R12: 0000000000000004
> [  123.007777] R13: ffffffff82d2cad8 R14: 0000000000000004 R15: 0000000000000000
> [  123.014906]  ? cpuidle_enter_state+0x97/0x460
> [  123.019270]  do_idle+0x1f1/0x230
> [  123.022502]  cpu_startup_entry+0x19/0x20
> [  123.026426]  start_secondary+0x172/0x1c0
> [  123.030352]  secondary_startup_64+0xb6/0xc0
> [  123.034536] handlers:
> [  123.036821] [<0000000054c59383>] usb_hcd_irq
> [  123.041106] [<000000006da712f0>] vfio_intx_handler [vfio_pci]
> [  123.046847] [<000000006da712f0>] vfio_intx_handler [vfio_pci]
> [  123.052592] [<000000006da712f0>] vfio_intx_handler [vfio_pci]
> [  123.058336] [<000000006da712f0>] vfio_intx_handler [vfio_pci]
> [  123.064090] [<000000006da712f0>] vfio_intx_handler [vfio_pci]
> [  123.069843] Disabling IRQ #16
> 
> Thanks,
> Alex
>  
> > > ---
> > > Changes since v1:
> > >  - move pcie_update_link_speed() to irq to prevent duplicate read of link_status
> > >  - Add Fixes: to commit message
> > >  
> > >  drivers/pci/pcie/bw_notification.c | 19 ++++++++++++++-----
> > >  1 file changed, 14 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/pci/pcie/bw_notification.c b/drivers/pci/pcie/bw_notification.c
> > > index d2eae3b7cc0f..c48746f1cf3c 100644
> > > --- a/drivers/pci/pcie/bw_notification.c
> > > +++ b/drivers/pci/pcie/bw_notification.c
> > > @@ -44,11 +44,10 @@ static void pcie_disable_link_bandwidth_notification(struct pci_dev *dev)
> > >  	pcie_capability_write_word(dev, PCI_EXP_LNKCTL, lnk_ctl);
> > >  }
> > >  
> > > -static irqreturn_t pcie_bw_notification_handler(int irq, void *context)
> > > +static irqreturn_t pcie_bw_notification_irq(int irq, void *context)
> > >  {
> > >  	struct pcie_device *srv = context;
> > >  	struct pci_dev *port = srv->port;
> > > -	struct pci_dev *dev;
> > >  	u16 link_status, events;
> > >  	int ret;
> > >  
> > > @@ -58,6 +57,17 @@ static irqreturn_t pcie_bw_notification_handler(int irq, void *context)
> > >  	if (ret != PCIBIOS_SUCCESSFUL || !events)
> > >  		return IRQ_NONE;
> > >  
> > > +	pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
> > > +	pcie_update_link_speed(port->subordinate, link_status);
> > > +	return IRQ_WAKE_THREAD;
> > > +}
> > > +
> > > +static irqreturn_t pcie_bw_notification_handler(int irq, void *context)
> > > +{
> > > +	struct pcie_device *srv = context;
> > > +	struct pci_dev *port = srv->port;
> > > +	struct pci_dev *dev;
> > > +
> > >  	/*
> > >  	 * Print status from downstream devices, not this root port or
> > >  	 * downstream switch port.
> > > @@ -67,8 +77,6 @@ static irqreturn_t pcie_bw_notification_handler(int irq, void *context)
> > >  		__pcie_print_link_status(dev, false);
> > >  	up_read(&pci_bus_sem);
> > >  
> > > -	pcie_update_link_speed(port->subordinate, link_status);
> > > -	pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
> > >  	return IRQ_HANDLED;
> > >  }
> > >  
> > > @@ -80,7 +88,8 @@ static int pcie_bandwidth_notification_probe(struct pcie_device *srv)
> > >  	if (!pcie_link_bandwidth_notification_supported(srv->port))
> > >  		return -ENODEV;
> > >  
> > > -	ret = request_threaded_irq(srv->irq, NULL, pcie_bw_notification_handler,
> > > +	ret = request_threaded_irq(srv->irq, pcie_bw_notification_irq,
> > > +				   pcie_bw_notification_handler,
> > >  				   IRQF_SHARED, "PCIe BW notif", srv);
> > >  	if (ret)
> > >  		return ret;
> > > -- 
> > > 2.19.2
> > >     
>