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    SubjectRe: AS spin lock bugs
    On Thu, Nov 13 2003, Nick Piggin wrote:
    >
    >
    > Jens Axboe wrote:
    >
    > >On Thu, Nov 13 2003, Jens Axboe wrote:
    > >
    > >>@@ -959,12 +960,12 @@
    > >> if (!aic)
    > >> return;
    > >>
    > >>- spin_lock(&aic->lock);
    > >>+ spin_lock_irqsave(&aic->lock, flags);
    > >> if (arq->is_sync == REQ_SYNC) {
    > >> set_bit(AS_TASK_IORUNNING, &aic->state);
    > >> aic->last_end_request = jiffies;
    > >> }
    > >>- spin_unlock(&aic->lock);
    > >>+ spin_unlock_irqrestore(&aic->lock, flags);
    > >>
    > >> put_io_context(arq->io_context);
    > >>}
    > >>
    > >
    > >BTW, this looks bogus. Why do you need any locking there?
    > >
    >
    > To prevent a request completion on another queue on another CPU from
    > racing with request insertion: last_end_request is undefined if the
    > flag is not set. I guess you could flip the statements and put a
    > smp_mb between them. Probably not worth the trouble though.

    No better to make it explicit, probably doesn't matter much in
    real-life. Thanks for the clarifications.

    --
    Jens Axboe

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