[Bug 1831252] Re: panic=-1 is completely ignored by the initrd causing unexpected behaviour

[Oliver Grawert]

targeting to xenial and bionic since we need this SRUed for Ubuntu Core
installs.

** Description changed:

  in Ubuntu Core we default to using panic=-1 on the kernel command line
  (documented at [1]) to speed up the auto-rollback mechanism of the
- kernel. on a kernel level this works just fine and teh system reboots
+ kernel. on a kernel level this works just fine and the system reboots
  immediately ...
  
  when in the initramfs during boot and a panic occurs, no reboot happens
  at all, the initrd spawns a shell regardless of the panic= value ...
  
  this is caused by a filter in  /usr/share/initramfs-tools/init
  
-         panic=*)
-                 panic="${x#panic=}"
-                 case ${panic} in
-                 *[![:digit:].]*)
-                         panic=
-                         ;;
-                 esac
-                 ;;
+         panic=*)
+                 panic="${x#panic=}"
+                 case ${panic} in
+                 *[![:digit:].]*)
+                         panic=
+                         ;;
+                 esac
+                 ;;
  
  this function only lets positive values through, else panic= simply gets
  unset
  
  the panic() function itself is also not capable of handling negative
  values, it has a sleep call that interprets negative values as
- commandline options instead of simply ignoring a negative sleep time
- [2].
+ commandline options instead of simply ignoring a negative sleep time [2]
+ (line 11).
  
  the filter in the init script should allow the -1 value (to comply with
  the kernel documentation and behaviour) and the panic() function should
  properly skip the sleep call when a negative value for panic= is set.
  
  [1] https://github.com/torvalds/linux/blob/v4.17/Documentation/admin-guide/kernel-parameters.txt#L2931
  [2] https://paste.ubuntu.com/p/mswD8Cd869/

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https://bugs.launchpad.net/bugs/1831252

Title:
  panic=-1 is completely ignored by the initrd causing unexpected
  behaviour

Status in initramfs-tools package in Ubuntu:
  New
Status in initramfs-tools source package in Xenial:
  New
Status in initramfs-tools source package in Bionic:
  New

Bug description:
  in Ubuntu Core we default to using panic=-1 on the kernel command line
  (documented at [1]) to speed up the auto-rollback mechanism of the
  kernel. on a kernel level this works just fine and the system reboots
  immediately ...

  when in the initramfs during boot and a panic occurs, no reboot
  happens at all, the initrd spawns a shell regardless of the panic=
  value ...

  this is caused by a filter in  /usr/share/initramfs-tools/init

          panic=*)
                  panic="${x#panic=}"
                  case ${panic} in
                  *[![:digit:].]*)
                          panic=
                          ;;
                  esac
                  ;;

  this function only lets positive values through, else panic= simply
  gets unset

  the panic() function itself is also not capable of handling negative
  values, it has a sleep call that interprets negative values as
  commandline options instead of simply ignoring a negative sleep time
  [2] (line 11).

  the filter in the init script should allow the -1 value (to comply
  with the kernel documentation and behaviour) and the panic() function
  should properly skip the sleep call when a negative value for panic=
  is set.

  [1] https://github.com/torvalds/linux/blob/v4.17/Documentation/admin-guide/kernel-parameters.txt#L2931
  [2] https://paste.ubuntu.com/p/mswD8Cd869/

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