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

    [ 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
    > >

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