From c89bcf3af01e7a8834cca5344e098bf879e99999 Mon Sep 17 00:00:00 2001 From: Alberto Garcia Date: Fri, 10 Nov 2017 20:54:47 +0200 Subject: [PATCH] block: Leave valid throttle timers when removing a BDS from a backend 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 are 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. [Fixed "There'a" typo as suggested by Max Reitz --Stefan] Reported-by: sochin jiang Signed-off-by: Alberto Garcia Reviewed-by: Max Reitz Message-id: e089c66e7c20289b046d782cea4373b765c5bc1d.1510339534.git.berto@igalia.com Signed-off-by: Stefan Hajnoczi --- block/block-backend.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/block/block-backend.c b/block/block-backend.c index df92a6280d..f10b1db612 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -655,15 +655,15 @@ BlockBackend *blk_by_public(BlockBackendPublic *public) */ void blk_remove_bs(BlockBackend *blk) { + ThrottleGroupMember *tgm = &blk->public.throttle_group_member; BlockDriverState *bs; - ThrottleTimers *tt; notifier_list_notify(&blk->remove_bs_notifiers, blk); - if (blk->public.throttle_group_member.throttle_state) { - tt = &blk->public.throttle_group_member.throttle_timers; + if (tgm->throttle_state) { bs = blk_bs(blk); bdrv_drained_begin(bs); - throttle_timers_detach_aio_context(tt); + throttle_group_detach_aio_context(tgm); + throttle_group_attach_aio_context(tgm, qemu_get_aio_context()); bdrv_drained_end(bs); } @@ -678,6 +678,7 @@ void blk_remove_bs(BlockBackend *blk) */ int blk_insert_bs(BlockBackend *blk, BlockDriverState *bs, Error **errp) { + ThrottleGroupMember *tgm = &blk->public.throttle_group_member; blk->root = bdrv_root_attach_child(bs, "root", &child_root, blk->perm, blk->shared_perm, blk, errp); if (blk->root == NULL) { @@ -686,10 +687,9 @@ int blk_insert_bs(BlockBackend *blk, BlockDriverState *bs, Error **errp) bdrv_ref(bs); notifier_list_notify(&blk->insert_bs_notifiers, blk); - if (blk->public.throttle_group_member.throttle_state) { - throttle_timers_attach_aio_context( - &blk->public.throttle_group_member.throttle_timers, - bdrv_get_aio_context(bs)); + if (tgm->throttle_state) { + throttle_group_detach_aio_context(tgm); + throttle_group_attach_aio_context(tgm, bdrv_get_aio_context(bs)); } return 0;