[PATCH v2 0/3] lockdep: liblockdep: Prevent chain_key collisions

[Alfredo Alvarez Fernandez]

This patch series prevents possible collisions in the chain_key
hashing macro iterate_chain_key(key1, key2) that can lead to lockdep
not detecting very simple deadlocks such as AA or ABBA.

The problem only affects the first allocated lock classes. That could
explain why it was not seen while running lockdep's test suite, since
by the time the test suite runs there are already registered lock
classes and the indexes allocated for the lock classes under test are
high enough to avoid collisions.

The patch series also extends the tools/liblockdep test suite with
tests covering the offending cases.

I came across the problem while testing a simple AA deadlock scenario
in userspace using a pthread_mutex and tools/liblockdep. In that
context it is fairly easy to have a clean and deterministic initial
state where the problem can be reproduced.

The proposed solution was tested with the newly introduced tests and
also with lockdep's test suite:
 [    0.000000] Good, all 253 testcases passed! |

v2:
  - Add detection for chain_key collisions under CONFIG_DEBUG_LOCKDEP.
    When a collision is detected the problem is reported and all lock
    debugging is turned off.

    Tested using liblockdep and the added tests before and after
    applying the fix, confirming both that the code added for the
    detection correctly reports the problem and that the fix actually
    fixes it.

    Tested tweaking lockdep to generate false collisions and
    verified that the problem is reported and that lock debugging is 
    turned off.

    Also tested with lockdep's test suite after applying the patch:
    [    0.000000] Good, all 253 testcases passed! |

  - Fix code style problems in added liblockdep tests

Alfredo Alvarez Fernandez (3):
  tools/liblockdep: add userspace version of READ_ONCE
  tools/liblockdep: add tests
  lockdep: prevent and detect chain_key collisions

 kernel/locking/lockdep.c                    | 73 ++++++++++++++++++++++-------
 tools/lib/lockdep/tests/AA.c                |  8 ++--
 tools/lib/lockdep/tests/ABA.c               | 13 +++++
 tools/lib/lockdep/tests/ABBA_2threads.c     | 46 ++++++++++++++++++
 tools/lib/lockdep/uinclude/linux/compiler.h |  1 +
 5 files changed, 121 insertions(+), 20 deletions(-)
 create mode 100644 tools/lib/lockdep/tests/ABA.c
 create mode 100644 tools/lib/lockdep/tests/ABBA_2threads.c

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2.5.0