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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Mon, 17 Oct 2016 09:53:49 +0200
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Subject: Re: [Qemu-devel] [PATCH 02/18] blockjob: introduce .drain callback
 for jobs
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: kwolf@redhat.com, qemu-block@nongnu.org, famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com



On 16/10/2016 12:02, Stefan Hajnoczi wrote:
> On Thu, Oct 13, 2016 at 07:34:06PM +0200, Paolo Bonzini wrote:
>> +static void backup_drain(BlockJob *job)
>> +{
>> +    BackupBlockJob *s = container_of(job, BackupBlockJob, common);
>> +
>> +    /* Need to keep a reference in case blk_drain triggers execution
>> +     * of backup_complete...
>> +     */
>> +    if (s->target) {
>> +        blk_ref(s->target);
>> +        blk_drain(s->target);
>> +        blk_unref(s->target);
>> +    }
> [...]
>> @@ -331,6 +346,7 @@ static void backup_complete(BlockJob *job, void *opaque)
>>      BackupCompleteData *data = opaque;
>>  
>>      blk_unref(s->target);
>> +    s->target = NULL;
> 
> Will blk_unref(s->target) segfault since backup_complete() has set it to
> NULL?  I expected backup_drain() to stash the pointer in a local
> variable to avoid using s->target.

Yes, indeed.

Paolo