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Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt

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On Sun, 2018-05-06 at 12:33 +1200, Ben Caradoc-Davies wrote:
> On 06/05/18 07:01, Ben Hutchings wrote:
> > I wonder if this is related to the recent RNG changes.  It seems that
> > many programs have started using blocking RNG functions like
> > getentropy(), and now that the kernel is more conservative in its
> > initial entropy estimation they can block for a long time.  Keyboard or
> > mouse input adds entropy.
> > At a guess, plymouth is starting the X server and the X server wants
> > random bits for MIT-MAGIC-COOKIE authentication.
> 
> Ben, I think you might be right. Only a few mouse wiggles are sufficient 
> to trigger the appearance of the plymouth LUKS screen. I guess that 
> mouse activity is a richer source of entropy than key presses.
> 
> So, where to from here? Should this be reassigned to plymouth or xorg?

Now that I've looked, it appears that Xorg is actually still using
/dev/urandom (via arc4random_buf() in libbsd).  So far as I know, reads
from /dev/urandom have historically succeeded without blocking, even
when there is very little entropy available.  Since many daemons depend
on this I think it has to be maintained.

But so far as I can see from the kernel code, that hasn't changed -
only the newer getentropy() function is more likely to block.  So I'm
quite confused.

Ben.

-- 
Ben Hutchings
If more than one person is responsible for a bug, no one is at fault.

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Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt (missing Kaby Lake firmware?) Ben Caradoc-Davies <ben@transient.nz> - 2018-05-03 04:10 +0200
  Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Caradoc-Davies <ben@transient.nz> - 2018-05-03 06:50 +0200
  Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Caradoc-Davies <ben@transient.nz> - 2018-05-03 07:30 +0200
  Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Caradoc-Davies <ben@transient.nz> - 2018-05-03 07:40 +0200
    Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Caradoc-Davies <ben@transient.nz> - 2018-05-04 01:40 +0200
    Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Caradoc-Davies <ben@transient.nz> - 2018-05-04 02:00 +0200
  Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Hutchings <ben@decadent.org.uk> - 2018-05-05 21:10 +0200
    Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Caradoc-Davies <ben@transient.nz> - 2018-05-06 02:40 +0200
      Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Hutchings <ben@decadent.org.uk> - 2018-05-06 05:10 +0200
    Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Laurent Bigonville <bigon@debian.org> - 2018-05-06 17:30 +0200
      Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt Ben Hutchings <ben@decadent.org.uk> - 2018-05-06 19:50 +0200
  Bug#897572: plymouth: long delay before splashscreen with kernel 4.16 Ben Caradoc-Davies <ben@transient.nz> - 2018-05-06 03:10 +0200
    Bug#897572: plymouth: long delay before splashscreen with kernel 4.16 at46 <at46n@t-online.de> - 2018-05-06 08:50 +0200
      Bug#897572: plymouth: long delay before splashscreen with kernel 4.16 Ben Caradoc-Davies <ben@transient.nz> - 2018-05-07 02:50 +0200
  Bug#897572:  Eric Mill <eric@konklone.com> - 2018-05-06 19:30 +0200
  Bug#897572: [PATCH] Revert "random: fix crng_ready() test" Ben Caradoc-Davies <ben@transient.nz> - 2018-05-07 05:10 +0200
    Bug#897572: [PATCH] Revert "random: fix crng_ready() test" "Theodore Y. Ts'o" <tytso@mit.edu> - 2018-05-07 06:20 +0200
  Bug#897572: [PATCH] Revert "random: fix crng_ready() test" Ben Caradoc-Davies <ben@transient.nz> - 2018-05-07 05:50 +0200
    Bug#897572: [PATCH] Revert "random: fix crng_ready() test" "Theodore Y. Ts'o" <tytso@mit.edu> - 2018-05-07 06:20 +0200
  Bug#897572: urandom hang in early boot Laurent Bigonville <bigon@debian.org> - 2018-05-07 19:40 +0200
    Bug#897572: urandom hang in early boot Ben Caradoc-Davies <ben@transient.nz> - 2018-05-08 01:20 +0200
      Bug#897572: urandom hang in early boot Ben Hutchings <ben@decadent.org.uk> - 2018-05-08 04:10 +0200
        Bug#897572: urandom hang in early boot Ben Caradoc-Davies <ben@transient.nz> - 2018-05-08 06:00 +0200
          Bug#897572: urandom hang in early boot Ben Caradoc-Davies <ben@transient.nz> - 2018-05-08 07:00 +0200
  Bug#897572: urandom hang in early boot Bjørn Mork <bjorn@mork.no> - 2018-05-08 13:40 +0200
    Bug#897572: urandom hang in early boot Yves-Alexis Perez <corsac@debian.org> - 2018-05-09 18:40 +0200
  Bug#897572: getrandom hang in early boot prevents plymouth passphrase entry Esokrates <esokrarkose@gmail.com> - 2018-05-09 11:00 +0200
  Bug#897572: [PATCH] Copy fontconfig .uuid files to avoid getrandom hang in early boot Ben Caradoc-Davies <ben@transient.nz> - 2018-05-10 02:00 +0200

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