On a DNE filesystem, an MDS can permanently deadlock its entire LDLM

blocking-AST (ldlm_bl) thread pool when a cross-MDT close is issued from lock

cancellation while the MDC import to the target MDT is not LUSTRE_IMP_FULL. All

lock cancellation on the affected MDS stops, the MDS begins evicting its own

internal client and then its regular clients, peer MDTs evict the affected MDS,

and the condition does not self-heal – only a reboot clears it.

Observed impact: on a 16-MDT production filesystem, two peer MDS entered this

state during failover of a third MDT. The filesystem was unusable for

approximately two hours and was recovered only by rebooting all MDS.