[RFC tip/locking/lockdep v5 00/17] lockdep: Support deadlock detection for recursive read locks

Boqun Feng
2018-02-22T07:05:51Z

Hi Ingo and Peter,

This is V5 for recursive read lock support in lockdep. The changes since
V4 are quite trivial:

* Fix some wording issues in patch #16 as pointed out by Randy
Dunlap

I added the explanation about reasoning in patch #16 in V4, which will
help understand this whole series. This patchset is based on v4.16-rc2.

Changes since V3:

* Reduce the unnecessary cost in structure lock_list as suggested
by Peter Zijlstra

* Add documentation for explanation of the reasoning in recursive
read lock deadlock detection.

* Add comments before bfs() describing the greedy search we use in
BFS for strong dependency paths.

* Add myself as a reviewer for LOCKING PRIMITIVES so that if there
is any performance regression, log misunderstanding or false
positives, people know who to blame^Wask help from.

V1: https://marc.info/?l=linux-kernel&m=150393341825453
V2: https://marc.info/?l=linux-kernel&m=150468649417950
V3: https://marc.info/?l=linux-kernel&m=150637795424969
V4: https://marc.info/?l=linux-kernel&m=151550860121565

As Peter pointed out:

https://marc.info/?l=linux-kernel&m=150349072023540

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

read_lock(A);
lock(B);
lock(B);
write_lock(A);

I got some inspiration from Gautham R Shenoy:

https://lwn.net/Articles/332801/

, 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
reported.

The whole series consists of 17 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. Redefine LOCK*_STATE*, now LOCK*_STATE_RR stand for recursive
read lock only and LOCK*_STATE 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.

14. Revert commit d82fed752942 ("locking/lockdep/selftests: Fix
mixed read-write ABBA tests"),

15. Reduce the extra size cost of lock_list to zero

16. Add documentation for recursive read lock deadlock detection
reasoning

17. Add myself as a LOCKING PRIMITIVES reviewer.

This series passed all the lockdep selftest cases(including those I
introduce).

Test and comments are welcome!

Regards,
Boqun