Messages in this thread | | | From | Boqun Feng <> | Subject | [RFC tip/locking/lockdep v5 00/17] lockdep: Support deadlock detection for recursive read locks | Date | Thu, 22 Feb 2018 15:08:47 +0800 |
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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
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