Messages in this thread | | | From | Boqun Feng <> | Subject | [RFC v7 00/19] lockdep: Support deadlock detection for recursive read locks | Date | Fri, 7 Aug 2020 15:42:19 +0800 |
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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@gmail.com/
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
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