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    Subject[PATCH] irq, x86: Remove IRQ_DISABLED check in process context IRQ move

    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.

    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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