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From:   "Elliott, Robert (Servers)" <elliott@hpe.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>
CC:     Ard Biesheuvel <ardb@kernel.org>, Taehee Yoo <ap420073@gmail.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
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Subject: RE: [PATCH] crypto: x86: Do not acquire fpu context for too long
Thread-Topic: [PATCH] crypto: x86: Do not acquire fpu context for too long
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Date:   Sun, 9 Oct 2022 19:58:58 +0000
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> -----Original Message-----
> From: Herbert Xu <herbert@gondor.apana.org.au>
> Sent: Sunday, October 9, 2022 1:20 AM
> To: Elliott, Robert (Servers) <elliott@hpe.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>; Taehee Yoo <ap420073@gmail.com>; li=
nux-
> crypto@vger.kernel.org; davem@davemloft.net; tglx@linutronix.de;
> mingo@redhat.com; bp@alien8.de; dave.hansen@linux.intel.com; x86@kernel.o=
rg;
> hpa@zytor.com; ebiggers@google.com
> Subject: Re: [PATCH] crypto: x86: Do not acquire fpu context for too long
>=20
> On Sat, Oct 08, 2022 at 07:48:07PM +0000, Elliott, Robert (Servers) wrote=
:
> >
> > Perhaps the cycles mode needs to call cond_resched() too?
>=20
> Yes, just make the cond_resched unconditional.  Having a few too many
> rescheds shouldn't be an issue.

This looks promising. I was able to trigger a lot of rcu stalls by setting:
  echo 2 > /sys/module/rcupdate/parameters/rcu_cpu_stall_timeout
  echo 200 > /sys/module/rcupdate/parameters/rcu_exp_cpu_stall_timeout

and running these concurrently:
  watch -n 0 modprobe tcrypt=3D200
  watch -n 0 module tcrypt=3D0 through 999

After changing tcrypt to call cond_resched in both cases, I don't see any
more rcu stalls.

I am getting miscompares from the extended self-test for crc32 and
crct10dif, and will investigate those further.

BTW, the way tcrypt always refuses to load leads to an ever-growing list in
the Call Traces:

kernel: Unloaded tainted modules: tcrypt():1 tcrypt():1 tcrypt():1 tcrypt()=
:1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt=
():1 tcrypt():1 t
crypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1=
 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt()=
:1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1
tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():=
1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt(=
):1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1
 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt()=
:1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt=
():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():
1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt(=
):1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt():1 tcryp=
t():1 tcrypt():1 tcrypt():1 tcrypt():1 tcrypt()
:1 tcrypt():1 tcrypt():1 tcrypt():1