Re: [Qemu-devel] [PATCH v2 2/2] QEMUBH: make AioContext's bh re-entrant

[Stefan Hajnoczi]

On Sun, Jun 16, 2013 at 07:21:21PM +0800, Liu Ping Fan wrote:
> @@ -47,8 +47,12 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void 
> *opaque)
>      bh->ctx = ctx;
>      bh->cb = cb;
>      bh->opaque = opaque;
> +    qemu_mutex_lock(&ctx->bh_lock);
>      bh->next = ctx->first_bh;
> +    /* Make sure the memebers ready before putting bh into list */

s/memebers/members/

> +    smp_wmb();

Why lock bh_lock before assigning bh->next?  Could you lock the mutex
here and then drop the smp_wmb() since the pthread function already does
that?

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_11