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authorEric Biggers <ebiggers@google.com>2017-11-07 14:15:27 -0800
committerHerbert Xu <herbert@gondor.apana.org.au>2017-11-10 19:20:26 +0800
commit1d9ddde12e3c9bab7f3d3484eb9446315e3571ca (patch)
treeb951622c25b368b0224012e2a463aee35c92d7da /kernel
parent63c53823f00f0ffd13e8c86b05c1486614a2df85 (diff)
download96b-common-1d9ddde12e3c9bab7f3d3484eb9446315e3571ca.tar.gz
lib/mpi: call cond_resched() from mpi_powm() loop
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. Do the cond_resched() once per bit rather than once per MPI limb because each limb might still easily take 100+ milliseconds on slow CPUs. Cc: <stable@vger.kernel.org> # v4.12+ Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'kernel')
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