Hi Ingo and Peter,
This is V3 for recursive read lock support in lockdep.
Changes since V2:
* Add one revert patch for commit d82fed752942
("locking/lockdep/selftests: Fix mixed read-write ABBA tests"),
since we could handle recursive read lock correctly, so we don't
need to fudge the test anymore.
* More document and print-message changes for redefining
LOCK*_STATE*.
* Rewrite some commit logs to improve the explanation of the idea.
V1: https://marc.info/?l=linux-kernel&m=150393341825453
V2: https://marc.info/?l=linux-kernel&m=150468649417950
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 is based on current master branch of tip tree:
a35205980288 ("Merge branch 'WIP.x86/fpu'")
, and I also put it at:
git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git arr-rfc-v3
The whole series consists of 14 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"),
This series passed all the lockdep selftest cases(including those I
introduce). Will play more other tests, and in the meanwhile hope to
hear your thoughts about this.
Test and comments are welcome!
Regards,
Boqun
