Linux kernel (drivers/infiniband/ulp/ipoib): The IPoIB multicast join task drops its lock mid-iteration, letting a

Impact

The IPoIB multicast join task drops its lock mid-iteration, letting a concurrent device flush move entries off the list it is walking. The loop then spins forever and the node hard-locks - observed in production on RHEL kernels. One fabric event during multicast activity takes the entire shared node offline, killing every tenant's workload on it.

Who can reach it

Driven by fabric and link events, not by a tenant device node: an IB port event, subnet-manager sweep, or link flap runs ipoib_ib_dev_flush_light concurrently with a multicast join. Any node running IPoIB with multicast groups is exposed; a tenant generating multicast join churn on the IPoIB interface widens the window. Conditional on the ib_ipoib module being in use.

What to do

No fixed version is recorded in this entry; boot a stable kernel carrying the mcast list locking fix (commits 4c8922ae8eb8 / 615e3adc2042). Interim: reduce IPoIB multicast usage on shared nodes and stabilise the fabric (avoid unnecessary port flaps / SM re-sweeps) until patched.

References