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SubjectRe: [PATCH] lib/mpi: call cond_resched() from mpi_powm() loop
On Mon, Nov 06, 2017 at 10:19:51PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> 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.
>
> Notwithstanding the insanity of doing this calculation in kernel mode
> rather than in userspace, fix it by calling cond_resched() as each bit
> from the exponent is processed. It's still noninterruptible, but at
> least it's preemptible now.
>
> Cc: stable@vger.kernel.org # v4.12+
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Patch applied. Thanks.
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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