Hello. I noticed that virtio_balloon is using register_oom_notifier() and leak_balloon() from virtballoon_oom_notify() might depend on __GFP_DIRECT_RECLAIM memory allocation. In leak_balloon(), mutex_lock(&vb->balloon_lock) is called in order to serialize against fill_balloon(). But in fill_balloon(), alloc_page(GFP_HIGHUSER[_MOVABLE] | __GFP_NOMEMALLOC | __GFP_NORETRY) is called with vb->balloon_lock mutex held. Since GFP_HIGHUSER[_MOVABLE] implies __GFP_DIRECT_RECLAIM | __GFP_IO | __GFP_FS, this allocation attempt might depend on somebody else's __GFP_DIRECT_RECLAIM | !__GFP_NORETRY memory allocation. Such __GFP_DIRECT_RECLAIM | !__GFP_NORETRY allocation can reach __alloc_pages_may_oom() and hold oom_lock mutex and call out_of_memory(). And leak_balloon() is called by virtballoon_oom_notify() via blocking_notifier_call_chain() callback when vb->balloon_lock mutex is already held by fill_balloon(). As a result, despite __GFP_NORETRY is specified, fill_balloon() can indirectly get stuck waiting for vb->balloon_lock mutex at leak_balloon(). Also, in leak_balloon(), virtqueue_add_outbuf(GFP_KERNEL) is called via tell_host(). Reaching __alloc_pages_may_oom() from this virtqueue_add_outbuf() request from leak_balloon() from virtballoon_oom_notify() from blocking_notifier_call_chain() from out_of_memory() leads to OOM lockup because oom_lock mutex is already held before calling out_of_memory(). OOM notifier callback should not (directly or indirectly) depend on __GFP_DIRECT_RECLAIM memory allocation attempt. Can you fix this dependency? _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
