Hi Ingo and Peter,
This is V6 for recursive read lock support in lockdep. I moved the
explanation about reasoning to patch #1, which will help understand this
whole series. This patchset is based on v4.16.
Other changes since V5:
* Rewrite the the explanation of the reasoning, focus on the proof
of equivalence between closed strong paths and deadlock
possiblity.
* Rewrite the detection for irq-safe->irq-unsafe check, not only
we support deadlock detection for recursive read locks, but also
save two BFS searchs (one backwards and one forwards) in the
detection. Thanks a lot for the discussion with Peter Zijlstra.
* Annotate SRCU related primitives with 'check' lockdep
annotations, so that we can detect deadlocks related to SRCU.
Also a self test case is added. The use case is provided by Paul
E. Mckenney.
* Make __bfs(.math) return bool, as suggested by Peter Zijlstra.
* Improve the readibliy of code based on good suggestions from
Peter Zijlstra. Hope this time nobody's brain gets hurted ;-)
* Minor fixes for typos.
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
V5: https://marc.info/?l=linux-kernel&m=151928315529363
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 20 patches:
1. Add documentation for recursive read lock deadlock detection
reasoning
2. Do a clean up on the return value of __bfs() and its friends.
3. 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.
4. 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.
5. Reduce the size of lock_list::distance.
6-7 Extend __bfs() to be able to traverse the stong dependency
patchs after recursive read locks added into the graph.
8. Make __bfs(.math) return bool.
9-11 Adjust check_redundant(), check_noncircular() and
check_irq_usage() with recursive read locks into consideration.
12. Finally add recursive read locks into the dependency graph.
13-14 Adjust lock cache chain key generation with recursive read locks
into consideration, and provide a test case.
15-16 Add more test cases.
17. Revert commit d82fed752942 ("locking/lockdep/selftests: Fix
mixed read-write ABBA tests"),
18. Add myself as a LOCKING PRIMITIVES reviewer.
19-20 Annotation SRCU correctly for deadlock detection, and provide a
test case.
This series passed all the lockdep selftest cases (including those I
introduce).
Test and comments are welcome!
Regards,
Boqun
