linux-kernel - [RFC tip/locking/lockdep v6 00/20] lockdep: Support deadlock detection for recursive read locks

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Date:   Wed, 11 Apr 2018 21:50:50 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andrea Parri <parri.andrea@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: [RFC tip/locking/lockdep v6 00/20] lockdep: Support deadlock detection for recursive read locks

Hi Ingo and Peter,

This is V6 for recursive read lock support in lockdep. I moved the
explanation about reasoning to patch #1, which will help understand this
whole series. This patchset is based on v4.16.

Other changes since V5:

*	Rewrite the the explanation of the reasoning, focus on the proof
	of equivalence between closed strong paths and deadlock
	possiblity.

*	Rewrite the detection for irq-safe->irq-unsafe check, not only
	we support deadlock detection for recursive read locks, but also
	save two BFS searchs (one backwards and one forwards) in the
	detection. Thanks a lot for the discussion with Peter Zijlstra.

*	Annotate SRCU related primitives with 'check' lockdep
	annotations, so that we can detect deadlocks related to SRCU.
	Also a self test case is added. The use case is provided by Paul
	E. Mckenney.

*	Make __bfs(.math) return bool, as suggested by Peter Zijlstra.

*	Improve the readibliy of code based on good suggestions from
	Peter Zijlstra. Hope this time nobody's brain gets hurted ;-)

*	Minor fixes for typos.

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


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 20 patches:

1.	Add documentation for recursive read lock deadlock detection
	reasoning

2.	Do a clean up on the return value of __bfs() and its friends.

3.	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.

4.	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.

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.	Add myself as a LOCKING PRIMITIVES reviewer.

19-20	Annotation SRCU correctly for deadlock detection, and provide a
	test case.

This series passed all the lockdep selftest cases (including those I
introduce).

Test and comments are welcome!

Regards,
Boqun