Re: [PATCH 11/33] aio: make aio_put_req() lockless

From: Jeff Moyer
Date: Fri Apr 12 2013 - 17:02:23 EST

Kent Overstreet <koverstreet@xxxxxxxxxx> writes:

> Freeing a kiocb needed to touch the kioctx for three things:
> * Pull it off the reqs_active list
> * Decrementing reqs_active
> * Issuing a wakeup, if the kioctx was in the process of being freed.
> This patch moves these to aio_complete(), for a couple reasons:
> * aio_complete() already has to issue the wakeup, so if we drop the
> kioctx refcount before aio_complete does its wakeup we don't have to
> do it twice.
> * aio_complete currently has to take the kioctx lock, so it makes sense
> for it to pull the kiocb off the reqs_active list too.
> * A later patch is going to change reqs_active to include unreaped
> completions - this will mean allocating a kiocb doesn't have to look
> at the ringbuffer. So taking the decrement of reqs_active out of
> kiocb_free() is useful prep work for that patch.
> This doesn't really affect cancellation, since existing (usb) code that
> implements a cancel function still calls aio_complete() - we just have
> to make sure that aio_complete does the necessary teardown for cancelled
> kiocbs.
> It does affect code paths where we free kiocbs that were never
> submitted; they need to decrement reqs_active and pull the kiocb off the
> reqs_active list. This occurs in two places: kiocb_batch_free(), which
> is going away in a later patch, and the error path in io_submit_one.

After reading the patch description and the patch, I'm left wondering
whether you did this as a cleanup or a performance patch.

Anyway, I don't see any issue with it.

Acked-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
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