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

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Date:   Wed, 6 Sep 2017 16:49:20 +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>
Subject: Re: [RFC tip/locking v2 00/13] lockdep: Support deadlock detection
 for recursive read locks

On Wed, Sep 06, 2017 at 04:28:11PM +0800, Boqun Feng wrote:
> 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

Hmm.. should revert

	d82fed752942 ("locking/lockdep/selftests: Fix mixed read-write ABBA tests")

for testing, as it is a work around because of we had limit support for
recursive read lock before.

I put a branch with that reverted at:

 	git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git arr-rfc-v2a

Selftest passed for that branch, now run it for more time.

Regards,
Boqun

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