Re: [patch] convert aio event reap to use atomic-op instead of spin_lock

On 4/11/07, Zach Brown <[email protected]> wrote:

> Sorry I wasn't thorough enough.  And partially because I was worried
> about changing structure type for user space facing struct aio_ring.
> Now that I looked through all arches, it looks safe as all arch's
> atomic_t has the same size as int.

> Here is the updated patch.

> @@ -144,7 +144,7 @@ struct kiocb {
>  struct aio_ring {
>       unsigned        id;     /* kernel internal index number */
>       unsigned        nr;     /* number of io_events */
> -     unsigned        head;
> +     atomic_t        head;
>       unsigned        tail;

Embedding an atomic_t in an ABI struct?  That makes everyone else
nervous too, right?

sure, make me nervous at least.

It may look safe on i386/x86-64 today, but this doesn't seem like wise
practice.  Is there any reason to believe that atomic_t will never
change size?  Does anything else do this already?

If nothing else, the "unsigned" (should be __u32, sigh) could be cast to
an atomic_t.

The atomic_t cast is equally iffy.  I don't know what would be a best solution.
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---

• References:
  • [patch] convert aio event reap to use atomic-op instead of spin_lock
    • From: [email protected] (Ken Chen)
  • Re: [patch] convert aio event reap to use atomic-op instead of spin_lock
    • From: Andrew Morton <[email protected]>
  • Re: [patch] convert aio event reap to use atomic-op instead of spin_lock
    • From: "Ken Chen" <[email protected]>
  • Re: [patch] convert aio event reap to use atomic-op instead of spin_lock
    • From: Zach Brown <[email protected]>

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