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    SubjectRe: [patch 1/2] genirq: Provide synchronize_hardirq()
    On Sat, Feb 15, 2014 at 12:55:18AM -0000, Thomas Gleixner wrote:
    > synchronize_irq() waits for hard irq and threaded handlers to complete
    > before returning. For some special cases we only need to make sure
    > that the hard interrupt part of the irq line is not in progress when
    > we disabled the - possibly shared - interrupt at the device level.
    >
    > A proper use case for this was provided by Russell. The sdhci driver
    > requires some irq triggered functions to be run in thread context. The
    > current implementation of the thread context is a sdio private kthread
    > construct, which has quite some shortcomings. These can be avoided
    > when the thread is directly associated to the device interrupt via the
    > generic threaded irq infrastructure.
    >
    > Though there is a corner case related to run time power management
    > where one side disables the device interrupts at the device level and
    > needs to make sure, that an already running hard interrupt handler has
    > completed before proceeding further. Though that hard interrupt
    > handler might wake the associated thread, which in turn can request
    > the runtime PM to reenable the device. Using synchronize_irq() leads
    > to an immediate deadlock of the irq thread waiting for the PM lock and
    > the synchronize_irq() waiting for the irq thread to complete.
    >
    > Due to the fact that it is sufficient for this case to ensure that no
    > hard irq handler is executing a new function which avoids the check
    > for the thread is required.
    >
    > Add a function, which just monitors the hard irq parts and ignores the
    > threaded handlers.
    >
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

    Acked-by: Peter Zijlstra <peterz@infradead.org>


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