On 04/08/2021 19:37, Paolo Bonzini wrote:
KVM creates a debugfs directory for each VM in order to store statistics
about the virtual machine. The directory name is built from the process
pid and a VM fd. While generally unique, it is possible to keep a
file descriptor alive in a way that causes duplicate directories, which
manifests as these messages:
[ 471.846235] debugfs: Directory '20245-4' with parent 'kvm' already present!
Even though this should not happen in practice, it is more or less
expected in the case of KVM for testcases that call KVM_CREATE_VM and
close the resulting file descriptor repeatedly and in parallel.
When this happens, debugfs_create_dir() returns an error but
kvm_create_vm_debugfs() goes on to allocate stat data structs which are
Rather the already allocated srructs leak, no?
The slow memory leak was spotted by syzkaller, where it
caused OOM reports.
I gave it a try and almost replied with "tested-by" but after running it over night I got 1 of these with followed OOM:
[ 1104.951394][ T544] debugfs: Directory '544-4' with parent 'kvm' already present!
[ 1104.951600][ T544] Failed to create 544-4
This is definitely an improvement as this used to happen a few times every hour but still puzzling :-/