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