[PATCH 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! |

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

 kernel/locking/lockdep.c                    | 14 ++++------
 tools/lib/lockdep/tests/AA.c                |  8 +++---
 tools/lib/lockdep/tests/ABA.c               | 13 +++++++++
 tools/lib/lockdep/tests/ABBA_2threads.c     | 43 +++++++++++++++++++++++++++++
 tools/lib/lockdep/uinclude/linux/compiler.h |  1 +
 5 files changed, 67 insertions(+), 12 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