linux-kernel - [RFC tip/locking v2 00/13] lockdep: Support deadlock detection for recursive read locks

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Date:   Wed,  6 Sep 2017 16:28:11 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Byungchul Park <byungchul.park@....com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: [RFC tip/locking v2 00/13] lockdep: Support deadlock detection for recursive read locks

Hi Ingo and Peter,

This is V2 for recursive read lock support in lockdep. I fix several
bugs in V1 and also add irq inversion detection support for recursive
read locks.

V1: https://marc.info/?l=linux-kernel&m=150393341825453


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 Linus' tree:

	e7d0c41ecc2e ("Merge tag 'devprop-4.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm")

, and I also put it at:

	git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git arr-rfc-v2

The whole series consists of 13 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.	Make lock state LOCK_*_READ stand for recursive read lock only
	and LOCK_* 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.

I did pass all the lockdep selftest cases(including those I introduce),
and now run it on one of my box, haven't shot my feet yet.

Test and comments are welcome!

Regards,
Boqun