Re: [PATCH v2] lib/mpi: call cond_resched() from mpi_powm() loop

From: David Howells
Date: Wed Nov 08 2017 - 07:50:25 EST


Eric Biggers <ebiggers3@xxxxxxxxx> wrote:

> On a non-preemptible kernel, if KEYCTL_DH_COMPUTE is called with the
> largest permitted inputs (16384 bits), the kernel spends 10+ seconds
> doing modular exponentiation in mpi_powm() without rescheduling. If all
> threads do it, it locks up the system. Moreover, it can cause
> rcu_sched-stall warnings.

Do you want this to go in immediately, or I should I push it to James for the
next merge window?

David