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    SubjectRe: IRQ and sleep_on
    christophe barbe wrote:
    >
    > I've missed the thread "avoiding bad sleeps" last week. I've had a similar problem
    > and I would like to discuss the solution I've used to avoid it.
    >
    > I want to wake up a sleeping process from an IRQ handler. In the process, if I use
    > a interruptible_sleep_on(), I need first to restore flags (otherwise the process
    > will sleep forever).
    >
    > restore_flags(flags);
    > // <<== here IRQ handler possibly call wake_up()
    > interruptible_sleep_on(&my_queue);
    >
    > [...]
    > I've written a modified version of interruptible_sleep_on which takes an
    > additionnal argument : flags to be restored.

    That's possible, but it will crash on Sparc: you cannot restore the
    interrupt flag saved in one function in another function.

    The solution is very simple: do not call restore_flags() before
    interruptible_sleep_on(), the schedule internally reenables interrupts.

    >>>>>>>>>>
    for(;;) {
    cli();
    if(condition) {
    sti();
    break;
    }
    interruptible_sleep_on();
    sti(); /* required! */
    }
    >>>>>>>>>

    But if you are writing new code, then DO NOT USE sleep_on(), use
    add_wait_queue(), and a spinlock instead of cli().
    Look at wait_event_irq in <linux/raid/md_k.h> from the 2.4 kernel as an
    example.

    --
    Manfred
    -
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