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Message-Id: <20180109143900.27475-1-boqun.feng@gmail.com>
Date: Tue, 9 Jan 2018 22:38:43 +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>,
Boqun Feng <boqun.feng@...il.com>
Subject: [RFC tip/locking/lockdep v4 00/17] lockdep: Support deadlock detection for recursive read locks
Hi Ingo and Peter,
This is V4 for recursive read lock support in lockdep. I add the
explanation about reasoning in patch #16 and would like to check that
with you first in case I made fundamental mistakes.
Changes since V3:
* Reduce the unnecessary cost in structure lock_list as suggested
by Peter Zijlstra
* Add documentation for explanation of the reasoning in recursive
read lock deadlock detection.
* Add comments before bfs() describing the greedy search we use in
BFS for strong dependency paths.
* Add myself as a reviewer for LOCKING PRIMITIVES so that if there
is any performance regression, log misunderstanding or false
positives, people know who to blame^Wask help from.
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
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 17 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"),
15. Reduce the extra size cost of lock_list to zero
16. Add documentation for recursive read lock deadlock detection
reasoning
17. Add myself as a LOCKING PRIMITIVES reviewer.
This series passed all the lockdep selftest cases(including those I
introduce).
Test and comments are welcome!
Regards,
Boqun
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