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From:   Gilad Ben-Yossef <gilad@benyossef.com>
Date:   Wed, 6 Nov 2019 09:33:20 +0200
Message-ID: <CAOtvUMc7pbtPAPUbEmz_MTHmB9LboQVdgG-t9tHCr=biEbFuUQ@mail.gmail.com>
Subject: Re: [PATCH 09/10] crypto: add timeout to crypto_wait_req
To:     Tero Kristo <t-kristo@ti.com>
Cc:     Herbert Xu <herbert@gondor.apana.org.au>,
        Eric Biggers <ebiggers@google.com>,
        David Miller <davem@davemloft.net>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        linux-omap@vger.kernel.org,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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On Wed, Nov 6, 2019 at 9:25 AM Tero Kristo <t-kristo@ti.com> wrote:
>
> On 06/11/2019 08:39, Gilad Ben-Yossef wrote:
> > Hi,
> >
> >
> > On Thu, Oct 17, 2019 at 3:26 PM Tero Kristo <t-kristo@ti.com> wrote:
> >>
> >> Currently crypto_wait_req waits indefinitely for an async crypto request
> >> to complete. This is bad as it can cause for example the crypto test
> >> manager to hang without any notification as to why it has happened.
> >> Instead of waiting indefinitely, add a 1 second timeout to the call,
> >> and provide a warning print if a timeout happens.
> >
> > While the incentive is clear and positive, this suggested solution
> > creates problems of its own.
> > In many (most?) cases where we are waiting here, we are waiting for a
> > DMA operation to finish from hardware.
> > Exiting while this pending DMA operation is not finished, even with a
> > proper error return value, is dangerous because
> > unless the calling code takes great care to not release the memory the
> > DMA is being done from/to, this can have disastrous effects.
> >
> > As Eric has already mentioned, one second might seem like a long time,
> > but we don't really know if it is enough.
> >
> > How about adding a second API (ig. crypto_wait_req_timeout) which
> > supports a calee specified timeout where
> > the calle knows how to correctly deal with timeout and port the
> > relevant call sites to use this?
>
> Yeah, that would work for me. I guess we could just swap the testmgr to
> use this timeout API, as it is quite clear it should timeout rather than
> wait indefinitely, and afaics, the data buffers it uses are limited
> size. It doesn't really matter for it whether the timeout is 1 second or
> 10 seconds, as long as it eventually times out.


As long as you avoid releasing the memory used on timeout, that should
work well, I think.

Gilad