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    SubjectRe: [PATCH 2/6] irq_work: Implement remote queueing
    On 06/25/2014 03:20 PM, Srivatsa S. Bhat wrote:
    > On 06/25/2014 03:09 PM, Peter Zijlstra wrote:
    >> On Wed, Jun 25, 2014 at 11:36:57AM +0200, Peter Zijlstra wrote:
    >>> On Wed, Jun 25, 2014 at 12:07:05PM +0530, Srivatsa S. Bhat wrote:
    >>>> I don't think irqs_disabled() is the problematic condition, since
    >>>> hotplug_cfg() invokes irq_work_run() from CPU_DYING context (which has
    >>>> irqs disabled). I guess you meant to remove the in_irq() check inside
    >>>> irq_work_run() instead?
    >>>
    >>> Yes, clearly I should not get up at 6am.. :-) Let me go do a new one.
    >>
    >> ---
    >> Subject: irq_work: Remove BUG_ON in irq_work_run()
    >> From: Peter Zijlstra <peterz@infradead.org>
    >> Date: Wed Jun 25 07:13:07 CEST 2014
    >>
    >> Because of a collision with 8d056c48e486 ("CPU hotplug, smp: flush any
    >> pending IPI callbacks before CPU offline"), which ends up calling
    >> hotplug_cfd()->flush_smp_call_function_queue()->irq_work_run(), which
    >> is not from IRQ context.
    >>
    >> Cc: Frederic Weisbecker <fweisbec@gmail.com>
    >> Reported-by: Stephen Warren <swarren@wwwdotorg.org>
    >> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    >> Link: http://lkml.kernel.org/n/tip-busatzs2gvz4v62258agipuf@git.kernel.org
    >> ---
    >> kernel/irq_work.c | 12 +-----------
    >> 1 file changed, 1 insertion(+), 11 deletions(-)
    >>
    >> Index: linux-2.6/kernel/irq_work.c
    >> ===================================================================
    >> --- linux-2.6.orig/kernel/irq_work.c
    >> +++ linux-2.6/kernel/irq_work.c
    >> @@ -160,21 +160,11 @@ static void irq_work_run_list(struct lli
    >> }
    >> }
    >>
    >> -static void __irq_work_run(void)
    >
    > Hmm, irq_work_cpu_notify() calls __irq_work_run() in the CPU_DYING
    > phase, to by-pass BUG_ON(!in_irq()). How about doing the same thing
    > from hotplug_cfd() as well?
    >

    Wait, that was a stupid idea. hotplug_cfd() already invokes irq_work_run
    indirectly via flush_smp_call_function_queue(). So irq_work_cpu_notify()
    doesn't need to invoke it again, AFAIU. So perhaps we can get rid of
    irq_work_cpu_notify() altogether?

    Regards,
    Srivatsa S. Bhat

    >> +static void irq_work_run(void)
    >> {
    >> irq_work_run_list(&__get_cpu_var(raised_list));
    >> irq_work_run_list(&__get_cpu_var(lazy_list));
    >> }
    >> -
    >> -/*
    >> - * Run the irq_work entries on this cpu. Requires to be ran from hardirq
    >> - * context with local IRQs disabled.
    >> - */
    >> -void irq_work_run(void)
    >> -{
    >> - BUG_ON(!in_irq());
    >> - __irq_work_run();
    >> -}
    >> EXPORT_SYMBOL_GPL(irq_work_run);
    >>
    >> /*
    >>
    >



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