Am 28.09.2017 um 19:01 hat Dr. David Alan Gilbert geschrieben: > Hi, > This is a 'fun' bug; I had a good chat to kwolf about it earlier. > A proper fix really needs to be done together with libvirt so that we > can sequence: > a) The stopping of the CPU on the source > b) The termination of the mirroring block job > c) The inactivation of the block devices on the source > (bdrv_inactivate_all) > d) The activation of the block devices on the destination > (bdrv_invalidate_cache_all) > e) The start of the CPU on the destinationOn 01/12/2018 03:21 PM, qemu-devel-confirm+7e23769bf079599cf1f3db6b00d347e8675d87f 3...@nongnu.org wrote: > > > It looks like you're hitting a race between b/c; we've had races > between c/d in the past and moved the bdrv_inactivate_all. > > During the discussion we ended up with two proposed solutions; > both of them require one extra command and one extra migration > capability. > > The block way > ------------- > 1) Add a new migration capability pause-at-complete > 2) Add a new migration state almost-complete > 3) After saving devices, if pause-at-complete is set, > transition to almost-complete > 4) Add a new command (migration-continue) that > causes the migration to inactivate the devices (c) > and send the final EOF to the destination. > > You set pause-at-complete, wait until migrate hits almost-complete; > cleanup the mirror job, and then do migration-continue. When it > completes do 'cont' on the destination. > > The migration way > ----------------- > 1) Stop doing (d) when the destination is started with -S > since it happens anyway when 'cont' is issued > 2) Add a new migration capability ext-manage-storage > 3) When 'ext-manage-storage' is set, we don't bother doing (c) > 4) Add a new command 'block-inactivate' on the source > > You set ext-manage-storage, do the migrate and when it's finished > clean up the block job, block-inactivate on the source, and > then cont on the destination. > > > My worry about the 'block way' is that the point at which we > do the pause seems pretty interesting; it probably is best > done after the final device save but before the inactivate, > but could be done before it. But it probably becomes API > and something might become dependent on where we did it. > > I think Kevin's worry about the 'migration way' is that > it's a bit of a block-specific fudge; which is probably right. > > > I've not really thought what happens when you have a mix of shared and > non-shared storage. > > Could we do any hack that isn't libvirt-visible for existing versions? > I guess maybe hack drive-mirror so it interlocks with the migration > code somehow to hold off on that inactivate? > > This code is visible probalby from 2.9.ish with the new locking code; > but really that b/c race has been there for ever - there's maybe > always the chance that the last few blocks of mirroring might have > happened too late ? > > Thoughts? > What are the libvirt view on the preferred solution. > > Dave
Devs, Did this issue ever get addressed? I'm looking at the history for mirror.c at https://github.com/qemu/qemu/commits/master/block/mirror.c and I don't see anything that leads me to believe this was fixed. I'm still unable to live migrate storage without risking corruption on even a moderately loaded vm. Thanks, schu