linux-kernel - Re: dm-crypt with no_read_workqueue and no_write

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Date:   Wed, 23 Dec 2020 21:09:55 +0000
From:   Ignat Korchagin <ignat@...udflare.com>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc:     Alasdair G Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        device-mapper development <dm-devel@...hat.com>,
        dm-crypt@...ut.de, linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Biggers <ebiggers@...nel.org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        kernel-team <kernel-team@...udflare.com>,
        Nobuto Murata <nobuto.murata@...onical.com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-crypto <linux-crypto@...r.kernel.org>
Subject: Re: dm-crypt with no_read_workqueue and no_write_workqueue + btrfs
 scrub = BUG()

On Wed, Dec 23, 2020 at 3:37 PM Maciej S. Szmigiero
<mail@...iej.szmigiero.name> wrote:
>
> On 14.12.2020 19:11, Maciej S. Szmigiero wrote:
> > Hi,
> >
> > I hit a reproducible BUG() when scrubbing a btrfs fs on top of
> > a dm-crypt device with no_read_workqueue and no_write_workqueue
> > flags enabled.
>
> Still happens on the current torvalds/master.
>
> Due to this bug it is not possible to use btrfs on top of
> a dm-crypt device with no_read_workqueue and no_write_workqueue
> flags enabled.
>
> @Ignat:
> Can you have a look at this as the person who added these flags?

I've been looking into this for the last couple of days because of
other reports [1].
Just finished testing a possible solution. Will submit soon.

> It looks like to me that the skcipher API might not be safe to
> call from a softirq context, after all.

It is less about skcipher API and more about how dm-crypt uses it as
well as some assumptions that it is always running in context which
can sleep.

> Maciej

Ignat

[1]: https://github.com/cloudflare/linux/issues/1