On 2017-11-10 19:54, Alberto Garcia wrote: > If a BlockBackend has I/O limits set then its ThrottleGroupMember > structure uses the AioContext from its attached BlockDriverState. > Those two contexts must be kept in sync manually. This is not > ideal and will be fixed in the future by removing the throttling > configuration from the BlockBackend and storing it in an implicit > filter node instead, but for now we have to live with this. > > When you remove the BlockDriverState from the backend then the > throttle timers are destroyed. If a new BlockDriverState is later > inserted then they are created again using the new AioContext. > > There'a a couple of problems with this: > > a) The code manipulates the timers directly, leaving the > ThrottleGroupMember.aio_context field in an inconsisent state. > > b) If you remove the I/O limits (e.g by destroying the backend) > when the timers are gone then throttle_group_unregister_tgm() > will attempt to destroy them again, crashing QEMU. > > While b) could be fixed easily by allowing the timers to be freed > twice, this would result in a situation in which we can no longer > guarantee that a valid ThrottleState has a valid AioContext and > timers. > > This patch ensures that the timers and AioContext are always valid > when I/O limits are set, regardless of whether the BlockBackend has a > BlockDriverState inserted or not. > > Reported-by: sochin jiang <sochin.ji...@huawei.com> > Signed-off-by: Alberto Garcia <be...@igalia.com> > --- > block/block-backend.c | 16 ++++++++-------- > 1 file changed, 8 insertions(+), 8 deletions(-)
Reviewed-by: Max Reitz <mre...@redhat.com>
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