tree d2eeea01b5c75ea3a14498b091085473259a98d4
parent 4640149fd566cc1f73fa4ac972220acdcbb05b81
author Mark Salyzyn <salyzyn@google.com> 1519152460 -0800
committer Mark Salyzyn <salyzyn@google.com> 1524085316 -0700

llkd: add live-lock daemon

Introduce a standalone live-lock daemon (llkd), to catch kernel
or native user space deadlocks and take mitigating actions.  Will
also configure [khungtaskd] to fortify the actions.

If a thread is in D or Z state with no forward progress for longer
than ro.llk.timeout_ms, or ro.llk.[D|Z].timeout_ms, kill the process
or parent process respectively.  If another scan shows the same
process continues to exist, then have a confirmed live-lock condition
and need to panic.  Panic the kernel in a manner to provide the
greatest bugreporting details as to the condition.  Add a alarm self
watchdog should llkd ever get locked up that is double the expected
time to flow through the mainloop.  Sampling is every
ro.llk_sample_ms.

Default will not monitor init, or [kthreadd] and all that [kthreadd]
spawns.  This reduces the effectiveness of llkd by limiting its
coverage.  If in the future, if value in covering kthreadd spawned
threads, the requirement will be to code drivers so that they do not
remain in a persistent 'D' state, or that they have mechanisms to
recover the thread should it be killed externally.  Then the
blacklists can be adjusted accordingly if these conditions are met.

An accompanying gTest set have been added, and will setup a persistent
D or Z process, with and without forward progress, but not in a
live-lock state because that would require a buggy kernel, or a module
or kernel modification to stimulate.

Android Properties llkd respond to (*_ms parms are in milliseconds):
- ro.config.low_ram default false, if true do not sysrq t (dump
  all threads).
- ro.llk.enable default false, allow live-lock daemon to be enabled.
- ro.khungtask.enable default false, allow [khungtaskd] to be enabled.
- ro.llk.mlockall default true, allow mlock'd live-lock daemon.
- ro.khungtask.timeout default 12 minutes.
- ro.llk.timeout_ms default 10 minutes, D or Z maximum timelimit,
  double this value and it sets the alarm watchdog for llkd.
- ro.llk.D.timeout_ms default ro.llk.timeout_ms, D maximum timelimit.
- ro.llk.Z.timeout_ms default ro.llk.timeout_ms, Z maximum timelimit.
- ro.llk.check_ms default 2 minutes sampling interval
  (ro.llk.timeout_ms / 5) for threads in D or Z state.
- ro.llk.blacklist.process default 0,1,2 (kernel, init and
  [kthreadd]), and process names (/comm or /cmdline) init,[kthreadd],
  lmkd,lmkd.llkd,llkd,[khungtaskd],watchdogd,[watchdogd],
  [watchdogd/0] ...
- ro.llk.blacklist.parent default 0,2 (kernel and [kthreadd]) and
  "[kthreadd]".  A comma separated lists of process ids, /comm names
  or /cmdline names.
- ro.llk.blacklist.uid default <empty>, comma separated list of
  uid numbers or names from getpwuid/getpwnam.

Test: llkd_unit_test
Bug: 33808187
Bug: 72838192
Change-Id: I32e8aa78aef10834e093265d0f3ed5b4199807c6