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Date: Wed, 11 Mar 2015 10:23:01 -0400
From: John Snow <jsnow@redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v2 04/17] qmp: Add
 block-dirty-bitmap-add and block-dirty-bitmap-remove
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: famz@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, armbru@redhat.com, vsementsov@parallels.com, stefanha@redhat.com



On 03/11/2015 09:58 AM, Stefan Hajnoczi wrote:
> On Mon, Mar 02, 2015 at 06:19:50PM -0500, John Snow wrote:
>> +static BdrvDirtyBitmap *block_dirty_bitmap_lookup(const char *node,
>> +                                                  const char *name,
>> +                                                  BlockDriverState **pbs,
>> +                                                  Error **errp)
>> +{
>> +    BlockDriverState *bs;
>> +    BdrvDirtyBitmap *bitmap;
>> +
>> +    if (!node) {
>> +        error_setg(errp, "Node cannot be NULL");
>> +        return NULL;
>> +    }
>> +    if (!name) {
>> +        error_setg(errp, "Bitmap name cannot be NULL");
>> +        return NULL;
>> +    }
>> +
>> +    bs = bdrv_lookup_bs(node, node, NULL);
>> +    if (!bs) {
>> +        error_setg(errp, "Node '%s' not found", node);
>> +        return NULL;
>> +    }
>> +
>> +    /* If caller provided a BDS*, provide the result of that lookup, too. */
>> +    if (pbs) {
>> +        *pbs = bs;
>> +    }
>> +
>> +    bitmap = bdrv_find_dirty_bitmap(bs, name);
>
> AioContext is not held here.  I'm worried that a block job (running
> under the AioContext) could change or delete the bitmap at the same time
> as this function is running.
>
> This function should acquire the AioContext before calling
> bdrv_find_dirty_bitmap() and fill out an AioContext** parameter so the
> caller can continue to use bs/bitmap under the lock.
>

OK, I'll audit all uses of this function with this in mind.