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Subject[RFC tip/locking v2 00/13] lockdep: Support deadlock detection for recursive read locks
Hi Ingo and Peter,

This is V2 for recursive read lock support in lockdep. I fix several
bugs in V1 and also add irq inversion detection support for recursive
read locks.


As Peter pointed out:

The lockdep current has a limit support for recursive read locks, the
deadlock case as follow could not be detected:


I got some inspiration from Gautham R Shenoy:

, and came up with this series.

The basic idea is:

* Add recursive read locks into the graph

* Classify dependencies into --(RR)-->, --(NR)-->, --(RN)-->,
--(NN)-->, where R stands for recursive read lock, N stands for
other locks(i.e. non-recursive read locks and write locks).

* Define strong dependency paths as the paths of dependencies
don't have two adjacent dependencies as --(*R)--> and --(R*)-->.

* Extend __bfs() to only traverse on strong dependency paths.

* If __bfs() finds a strong dependency circle, then a deadlock is

The whole series is based on current master branch of Linus' tree:

e7d0c41ecc2e ("Merge tag 'devprop-4.14-rc1' of git://")

, and I also put it at:

git:// arr-rfc-v2

The whole series consists of 13 patches:

1. Do a clean up on the return value of __bfs() and its friends.

2. Make __bfs() able to visit every dependency until a match is
found. The old version of __bfs() could only visit each lock
class once, and this is insufficient if we are going to add
recursive read locks into the dependency graph.

3. Make lock state LOCK_*_READ stand for recursive read lock only
and LOCK_* stand for write lock and non-recursive read lock.

4-5 Extend __bfs() to be able to traverse the stong dependency
patchs after recursive read locks added into the graph.

6-8 Adjust check_redundant(), check_noncircular() and
check_irq_usage() with recursive read locks into consideration.

9. Finally add recursive read locks into the dependency graph.

10-11 Adjust lock cache chain key generation with recursive read locks
into consideration, and provide a test case.

12-13 Add more test cases.

I did pass all the lockdep selftest cases(including those I introduce),
and now run it on one of my box, haven't shot my feet yet.

Test and comments are welcome!


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