[libvirt] [RFC PATCH] qcow2: Fix race in cache invalidation
Alexey Kardashevskiy
aik at ozlabs.ru
Thu Sep 25 12:29:36 UTC 2014
On 09/25/2014 08:20 PM, Kevin Wolf wrote:
> Am 25.09.2014 um 11:55 hat Alexey Kardashevskiy geschrieben:
>> Right. Cool. So is below what was suggested? I am doublechecking as it does
>> not solve the original issue - the bottomhalf is called first and then
>> nbd_trip() crashes in qcow2_co_flush_to_os().
>>
>> diff --git a/block.c b/block.c
>> index d06dd51..1e6dfd1 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -5037,20 +5037,22 @@ void bdrv_invalidate_cache(BlockDriverState *bs,
>> Error **errp)
>> if (local_err) {
>> error_propagate(errp, local_err);
>> return;
>> }
>>
>> ret = refresh_total_sectors(bs, bs->total_sectors);
>> if (ret < 0) {
>> error_setg_errno(errp, -ret, "Could not refresh total sector count");
>> return;
>> }
>> +
>> + bdrv_drain_all();
>> }
>
> Try moving the bdrv_drain_all() call to the top of the function (at
> least it must be called before bs->drv->bdrv_invalidate_cache).
Ok, I did. Did not help.
>
>> +static QEMUBH *migration_complete_bh;
>> +static void process_incoming_migration_complete(void *opaque);
>> +
>> static void process_incoming_migration_co(void *opaque)
>> {
>> QEMUFile *f = opaque;
>> - Error *local_err = NULL;
>> int ret;
>>
>> ret = qemu_loadvm_state(f);
>> qemu_fclose(f);
>
> Paolo suggested to move eveything starting from here, but as far as I
> can tell, leaving the next few lines here shouldn't hurt.
Ouch. I was looking at wrong qcow2_fclose() all this time :)
Aaaany what you suggested did not help -
bdrv_co_flush() calls qemu_coroutine_yield() while this BH is being
executed and the situation is still the same.
>
>> free_xbzrle_decoded_buf();
>> if (ret < 0) {
>> error_report("load of migration failed: %s", strerror(-ret));
>> exit(EXIT_FAILURE);
>> }
>> qemu_announce_self();
>>
>> bdrv_clear_incoming_migration_all();
>> +
>> + migration_complete_bh = aio_bh_new(qemu_get_aio_context(),
>> + process_incoming_migration_complete,
>> + NULL);
>> + qemu_bh_schedule(migration_complete_bh);
>> +}
>> +
>> +static void process_incoming_migration_complete(void *opaque)
>> +{
>> + Error *local_err = NULL;
>> +
>> /* Make sure all file formats flush their mutable metadata */
>> bdrv_invalidate_cache_all(&local_err);
>> if (local_err) {
>> qerror_report_err(local_err);
>> error_free(local_err);
>> exit(EXIT_FAILURE);
>> }
>>
>> if (autostart) {
>> vm_start();
>> } else {
>> runstate_set(RUN_STATE_PAUSED);
>> }
>> + qemu_bh_delete(migration_complete_bh);
>> + migration_complete_bh = NULL;
>> }
>
> That part looks good to me. I hope moving bdrv_drain_all() does the
> trick, otherwise there's somthing wrong with our reasoning.
>
> Kevin
>
--
Alexey
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