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...ote: we only let refcount go to 0 on device release. This works well but we now access the ref counter twice so there's a race: all users might see a high count and decide to defer freeing resources. In the end no one initiates freeing resources until the last reference is gone (which is on VM shotdown so might happen after a looooong time). Let's do what we probably should have done straight away: switch from kref to plain atomic, documenting the semantics, return the refcount value atomically after decrement, then use that to avoid the deadlock. Reported-by: Qin Chuanyu <qinchuanyu at...

...ote: we only let refcount go to 0 on device release. This works well but we now access the ref counter twice so there's a race: all users might see a high count and decide to defer freeing resources. In the end no one initiates freeing resources until the last reference is gone (which is on VM shotdown so might happen after a looooong time). Let's do what we probably should have done straight away: switch from kref to plain atomic, documenting the semantics, return the refcount value atomically after decrement, then use that to avoid the deadlock. Reported-by: Qin Chuanyu <qinchuanyu at...

This fixes a deadlock with vhost reported in the field, as well as a theoretical race issue found by code review. Patches 1+2 are needed for stable. Thanks to Qin Chuanyu for reporting the issue! Michael S. Tsirkin (3): kref: add kref_sub_return vhost: fix ref cnt checking deadlock vhost: fix a theoretical race in device cleanup include/linux/kref.h | 33

This fixes a deadlock with vhost reported in the field, as well as a theoretical race issue found by code review. Patches 1+2 are needed for stable. Thanks to Qin Chuanyu for reporting the issue! Michael S. Tsirkin (3): kref: add kref_sub_return vhost: fix ref cnt checking deadlock vhost: fix a theoretical race in device cleanup include/linux/kref.h | 33