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From: Alberto Garcia <berto@igalia.com>
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Date: Thu, 14 Feb 2019 16:21:55 +0100
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Subject: Re: [Qemu-devel] [PATCH 02/13] block: Freeze the backing chain for
 the duration of the commit job
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To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz <mreitz@redhat.com>

On Tue 12 Feb 2019 03:54:15 PM CET, Kevin Wolf wrote:
>> @@ -336,6 +340,10 @@ void commit_start(const char *job_id, BlockDriverState *bs,
>>          }
>>      }
>>  
>> +    if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
>> +        goto fail;
>> +    }
>
> Don't error paths need to unfreeze after this?

Yes, and while debugging this I realized that the error path is wrong:

    if (commit_top_bs) {
        bdrv_replace_node(commit_top_bs, top, &error_abort);
    }
    job_early_fail(&s->common.job);

Doing bdrv_replace_node() here before job_early_fail() fails with

Unexpected error in bdrv_check_update_perm() at block.c:1920:
Conflicts with use by commit job 'virtio0' as 'intermediate node', which does not allow 'consistent read' on <node-name>
Aborted

I'll write a separate patch for this problem.

Berto