linux-kernel - Re: [PATCH v2] lib/mpi: call cond_resched() from mpi

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Message-ID: <25888.1510145417@warthog.procyon.org.uk>
Date:   Wed, 08 Nov 2017 12:50:17 +0000
From:   David Howells <dhowells@...hat.com>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     dhowells@...hat.com, linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Tudor-Dan Ambarus <tudor.ambarus@...rochip.com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Salvatore Benedetto <salvatore.benedetto@...el.com>,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        Eric Biggers <ebiggers@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] lib/mpi: call cond_resched() from mpi_powm() loop

Eric Biggers <ebiggers3@...il.com> 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