Current mainline git (24e700e291d52bd2) hangs when building e.g. perf

[Markus Trippelsdorf]

Current mainline git (24e700e291d52bd2) hangs when building software
concurrently (for example perf).
The issue is not 100% reproducible (sometimes building perf succeeds),
so bisecting will not work.
Magic SysRq key doesn't work and there is nothing in the logs.
Enabling CONFIG_PROVE_LOCKING makes the issue go away.

Any ideas on how to debug this further?

-- 
Markus