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

[liu ping fan]

On Mon, Jun 17, 2013 at 11:28 PM, Stefan Hajnoczi <address@hidden> wrote:
> 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/
>
Will fix, thanks.
>> +    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?
>
As Paolo's explain, it will open race gap for writers.

Thanks and regards,
Pingfan
> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_11