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    SubjectRe: [patch] aio: fix buggy put_ioctx call in aio_complete
    ==> Regarding RE: [patch] aio: fix buggy put_ioctx call in aio_complete; "Chen, Kenneth W" <> adds:

    kenneth.w.chen> wrote on Thursday, December 21, 2006 8:56
    kenneth.w.chen> AM I think I'm going to abandon this whole synchronize
    kenneth.w.chen> thing and going to put the wake up call inside ioctx_lock
    kenneth.w.chen> spin lock along with the other patch you mentioned above in
    kenneth.w.chen> the waiter path. On top of that, I have another patch
    kenneth.w.chen> attempts to perform wake-up only when the waiter can truly
    kenneth.w.chen> proceed in aio_read_evt so dribbling I/O completion doesn't
    kenneth.w.chen> inefficiently waking up waiter too frequently and only to
    kenneth.w.chen> have waiter put back to sleep again. I will dig that up and
    kenneth.w.chen> experiment.
    >> In the mean time, can't we simply take the context lock in
    >> wait_for_all_aios? Unless I missed something, I think that will address
    >> the reference count problem.

    kenneth.w.chen> Take ioctx_lock is one part, the other part is to move

    kenneth.w.chen> spin_unlock_irqrestore(&ctx->ctx_lock, flags);

    kenneth.w.chen> in aio_complete all the way down to the end of the
    kenneth.w.chen> function, after wakeup and put_ioctx. But then the ref
    kenneth.w.chen> counting on ioctx in aio_complete path is Meaningless,
    kenneth.w.chen> which is the thing I'm trying to remove.

    OK, right. But are we simply papering over the real problem? Earlier in
    this thread, you stated:

    > flush_workqueue() is not allowed to be called in the softirq context.
    > However, aio_complete() called from I/O interrupt can potentially call
    > put_ioctx with last ref count on ioctx and trigger a bug warning. It
    > is simply incorrect to perform ioctx freeing from aio_complete.

    But how do we end up with the last reference to the ioctx in the aio
    completion path? That's a question I haven't seen answered.

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