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    SubjectRe: [PATCH v2] PCI: dra7xx: mark dra7xx_pcie_msi irq as IRQF_NO_THREAD
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    On 12/04/2015 08:46 PM, Bjorn Helgaas wrote:
    > Hi Grygorii,
    >
    > On Fri, Nov 20, 2015 at 03:59:26PM +0200, Grygorii Strashko wrote:
    >> On -RT, TI DRA7 PCIe driver always produces below backtrace when the
    >> first PCI interrupt is triggered:
    >>
    >> ------------[ cut here ]------------
    >> WARNING: CPU: 1 PID: 82 at kernel/irq/handle.c:150 handle_irq_event_percpu+0x14c/0x174()
    >> irq 460 handler irq_default_primary_handler+0x0/0x14 enabled interrupts
    [...]
    >> [<c00891b0>] (handle_simple_irq) from [<c0085514>] (generic_handle_irq+0x30/0x44)
    >> r5:ee4a9020 r4:000001cc
    >> [<c00854e4>] (generic_handle_irq) from [<c034a7d4>] (dra7xx_pcie_msi_irq_handler+0x7c/0x8c)
    >> r5:ee4a9020 r4:00000001
    >> [<c034a758>] (dra7xx_pcie_msi_irq_handler) from [<c0086f08>] (irq_forced_thread_fn+0x28/0x5c)
    >> r5:ee1d0900 r4:ee4b59c0
    >> [<c0086ee0>] (irq_forced_thread_fn) from [<c00871dc>] (irq_thread+0x128/0x204)
    >> r7:00000001 r6:00000000 r5:ee4d2000 r4:ee4b59e4
    >> [<c00870b4>] (irq_thread) from [<c005e2fc>] (kthread+0xd4/0xec)
    >> r10:00000000 r9:00000000 r8:00000000 r7:c00870b4 r6:ee4b59c0 r5:ee4b5a00
    >> r4:00000000
    >> [<c005e228>] (kthread) from [<c000faa8>] (ret_from_fork+0x14/0x2c)
    >> r7:00000000 r6:00000000 r5:c005e228 r4:ee4b5a00
    >> ---[ end trace 0000000000000002 ]---
    >
    > The backtrace might be OK (maybe slightly overkill), but all the
    > stack addresses are certainly irrelevant and distracting. We only
    > need enough to recognize the problem. I don't think the modules list
    > is relevant either.

    I'll take this into account. Is this blocker for this patch now?

    >
    >> This backtrace is triggered because dra7xx_pcie_msi_irq_handler()
    >> forced to be threaded by default on -RT but, in the same time, it's
    >> IRQ dispatcher and calls generic_handle_irq(), which leads to
    >> handle_simple_irq() call. The handle_simple_irq() expected to be
    >> called with IRQ disabled.
    >>
    >> The same issue will also happen if kernel will boot with "threadirqs"
    >> cmdline parameter (CONFIG_IRQ_FORCED_THREADING).
    >>
    >> As discussed in [1], the current DRA7 PCIe hw configuration supports
    >> 32 interrupts, which cannot change because it's hardwired in silicon,
    >> this is a single status read and assuming that only a few (most of the
    >> time it will be exactly ONE) of those interrupts are pending at the
    >> same time is pretty much a sane assumption. And recommended fix for
    >> this issue is to request dra7xx_pcie_msi IRQ with IRQF_NO_THREAD flag.
    >>
    >> [1] https://lkml.org/lkml/2015/11/3/660
    >>
    >> Cc: Thomas Gleixner <tglx@linutronix.de>
    >> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    >> Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
    >> ---
    >> Changes in v2:
    >> - comment in code truncated
    >> Link on v1:
    >> https://lkml.org/lkml/2015/11/5/593
    >> drivers/pci/host/pci-dra7xx.c | 13 ++++++++++++-
    >> 1 file changed, 12 insertions(+), 1 deletion(-)
    >>
    >> diff --git a/drivers/pci/host/pci-dra7xx.c b/drivers/pci/host/pci-dra7xx.c
    >> index 8c36880..0415192 100644
    >> --- a/drivers/pci/host/pci-dra7xx.c
    >> +++ b/drivers/pci/host/pci-dra7xx.c
    >> @@ -301,8 +301,19 @@ static int __init dra7xx_add_pcie_port(struct dra7xx_pcie *dra7xx,
    >> return -EINVAL;
    >> }
    >>
    >> + /*
    >> + * Mark dra7xx_pcie_msi IRQ as IRQF_NO_THREAD
    >> + * On -RT and if kernel is booting with "threadirqs" cmd line parameter
    >> + * the dra7xx_pcie_msi_irq_handler() will be forced threaded but,
    >> + * in the same time, it's IRQ dispatcher and calls generic_handle_irq(),
    >> + * which, in turn, will be resolved to handle_simple_irq() call.
    >> + * The handle_simple_irq() expected to be called with IRQ disabled, as
    >> + * result kernle will display warning:
    >> + * "irq XXX handler YYY+0x0/0x14 enabled interrupts".
    >> + */
    >> ret = devm_request_irq(&pdev->dev, pp->irq,
    >> - dra7xx_pcie_msi_irq_handler, IRQF_SHARED,
    >> + dra7xx_pcie_msi_irq_handler,
    >> + IRQF_SHARED | IRQF_NO_THREAD,
    >> "dra7-pcie-msi", pp);
    >
    > There's similar code in exynos_add_pcie_port(), imx6_add_pcie_port(),
    > and spear13xx_add_pcie_port(). Do they need similar changes? If not,
    > why not?
    >
    > I see your discussion about DRA7 hardware design, but my impression is
    > that this problem affects anybody who calls dw_handle_msi_irq() from a
    > handler registered with IRQF_SHARED.

    Issue fixed by this patch is not related to IRQF_SHARED.
    It will happen on -RT or if kernel will boot with "threadirqs" cmd line parameter
    - in both cases these PCI IRQ handlers will be forced to be threaded and,
    as result, generic_handle_irq() will produce above backtrace.

    Personally, I don't have strong opinion about "should similar change be applied
    to other PCI drivers or not?" And I think, that owners of those driver should
    make such decision.

    --
    regards,
    -grygorii


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