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    SubjectRe: [PATCH] irq, x86: Remove IRQ_DISABLED check in process context IRQ move
    "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com> writes:

    > As discussed in the thread here
    > http://marc.info/?l=linux-kernel&m=123964468521142&w=2
    >
    > On Fri, Apr 10, 2009 at 3:02 PM, Eric W. Biederman
    > <ebiederm@xmission.com> wrote:
    >>
    >> It looks like some additional bugs have slipped in since last I looked.
    >>
    >> set_irq_affinity does this:
    >> ifdef CONFIG_GENERIC_PENDING_IRQ
    >> if (desc->status & IRQ_MOVE_PCNTXT || desc->status & IRQ_DISABLED) {
    >> cpumask_copy(desc->affinity, cpumask);
    >> desc->chip->set_affinity(irq, cpumask);
    >> } else {
    >> desc->status |= IRQ_MOVE_PENDING;
    >> cpumask_copy(desc->pending_mask, cpumask);
    >> }
    >> #else
    >>
    >> That IRQ_DISABLED case is a software state and as such it has nothing to
    >> do with how safe it is to move an irq in process context.
    >>
    >
    > "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com> writes:
    >> On Sat, 2009-04-11 at 04:01 -0700, Eric W. Biederman wrote:
    >> >
    >> > If the goal is moving MSIs, we should modify the msi code to be safe
    >> > in process context and to set IRQ_MOVE_PCNTXT.
    >> >
    >> > The only reason we migrate MSIs in interrupt context today is that there
    >> > wasn't infrastructure for support migration both in interrupt context
    >> > and outside of it.
    >>
    >> Yes. The idea here was to force the MSI migration to happen in process
    >> context. One of the patches in the series did
    >>
    >> disable_irq(dev->irq);
    >> irq_set_affinity(dev->irq, cpumask_of(dev->cpu));
    >> enable_irq(dev->irq);
    >>
    >> with the above patch adding irq/manage code check for interrupt disabled
    >> and moving the interrupt in process context.
    >>
    >> IIRC, there was no IRQ_MOVE_PCNTXT when we were developing this HPET
    >> code and we ended up having this ugly hack. IRQ_MOVE_PCNTXT was there
    >> when we eventually submitted the patch upstream. But, looks like I did a
    >> blind rebasing instead of using IRQ_MOVE_PCNTXT in hpet MSI code. That
    >> was my fault. Will send a patch to fix this ugliness.
    >
    > Below patch fixes this. i.e., revert
    > commit 932775a4ab622e3c99bd59f14cc7d96722f79501
    > and add PCNTXT to HPET MSI setup. Also removes copying of desc->affinity
    > in generic code as set_affinity routines are doing it internally.

    Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

    This looks good.

    Do you think you could take this one step farther, place a read
    after the hpet_msi_write to flush the write to the interrupt source,
    and then finish up the work to change the irq reception setup?

    Roughly like ir_set_msi_irq_affinity?

    That way we really do get everything done in process context.

    > Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
    > ---
    > arch/x86/kernel/apic/io_apic.c | 2 ++
    > kernel/irq/manage.c | 5 ++---
    > 2 files changed, 4 insertions(+), 3 deletions(-)
    >
    > diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
    > index 767fe7e..aaf8212 100644
    > --- a/arch/x86/kernel/apic/io_apic.c
    > +++ b/arch/x86/kernel/apic/io_apic.c
    > @@ -3667,12 +3667,14 @@ int arch_setup_hpet_msi(unsigned int irq)
    > {
    > int ret;
    > struct msi_msg msg;
    > + struct irq_desc *desc = irq_to_desc(irq);
    >
    > ret = msi_compose_msg(NULL, irq, &msg);
    > if (ret < 0)
    > return ret;
    >
    > hpet_msi_write(irq, &msg);
    > + desc->status |= IRQ_MOVE_PCNTXT;
    > set_irq_chip_and_handler_name(irq, &hpet_msi_type, handle_edge_irq,
    > "edge");
    >
    > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
    > index 7e2e7dd..2734eca 100644
    > --- a/kernel/irq/manage.c
    > +++ b/kernel/irq/manage.c
    > @@ -109,10 +109,9 @@ int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask)
    > spin_lock_irqsave(&desc->lock, flags);
    >
    > #ifdef CONFIG_GENERIC_PENDING_IRQ
    > - if (desc->status & IRQ_MOVE_PCNTXT || desc->status & IRQ_DISABLED) {
    > - cpumask_copy(desc->affinity, cpumask);
    > + if (desc->status & IRQ_MOVE_PCNTXT)
    > desc->chip->set_affinity(irq, cpumask);
    > - } else {
    > + else {
    > desc->status |= IRQ_MOVE_PENDING;
    > cpumask_copy(desc->pending_mask, cpumask);
    > }
    > --
    > 1.6.0.6


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