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Date: Fri, 10 Nov 2017 22:37:30 +1100 From: Herbert Xu <herbert@...dor.apana.org.au> To: Eric Biggers <ebiggers3@...il.com> Cc: linux-crypto@...r.kernel.org, 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] 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@...gle.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@...r.kernel.org # v4.12+ > Signed-off-by: Eric Biggers <ebiggers@...gle.com> Patch applied. Thanks. -- Email: Herbert Xu <herbert@...dor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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