Hi Peter and Waiman, As promised, this is the updated version of my previous lockdep patchset for recursive read lock support. It's based on v5.8. Previous versions can be found at: 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 V6: https://lore.kernel.org/lkml/20180411135110.9217-1-boqun.feng@xxxxxxxxx/ Changes since last version: * I change the detection algorithm which I present in 2018 plumbers [1], you can find the explanation of the detection method in patch #2. * Adjust the irq safe->unsafe changes from Frederic Weisbecker * Add more tests. 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 -(SR)->, -(ER)->, -(SN)->, -(EN)->, where R stands for recursive read lock, N stands for other locks(i.e. non-recursive read locks and write locks), S stands for shared locks (read locks, no matter recursive or not), and E stands for exclusive locks (i.e. write locks) * Define strong dependency paths as the paths of dependencies don't have two adjacent dependencies as -(*R)-> and -(S*)->. * 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 19 patches: 1. Add documentation for recursive read lock deadlock detection reasoning 2. Annotate read_lock() correctly (with queued_read_lock() semantics into consideration) 3. Do a clean up on the return value of __bfs() and its friends. 4. 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. 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"), 18-19 Add more test cases (including tests that are specific for queued_read_lock()) This series passed all the lockdep selftest cases (including those I introduce). Test and comments are welcome! Regards, Boqun
