From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753133AbeDKNrR (ORCPT ); Wed, 11 Apr 2018 09:47:17 -0400 Received: from mail-wr0-f175.google.com ([209.85.128.175]:43771 "EHLO mail-wr0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751699AbeDKNrP (ORCPT ); Wed, 11 Apr 2018 09:47:15 -0400 X-Google-Smtp-Source: AIpwx4/sawW5t/AHNUEtwVf7vldWK704RfAfln+EZxnEH4wNi8jNhlRaH0OXqliJs5G4usKCJaRCOw== X-ME-Sender: From: Boqun Feng To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Ingo Molnar , Andrea Parri , "Paul E. McKenney" , Boqun Feng Subject: [RFC tip/locking/lockdep v6 00/20] lockdep: Support deadlock detection for recursive read locks Date: Wed, 11 Apr 2018 21:50:50 +0800 Message-Id: <20180411135110.9217-1-boqun.feng@gmail.com> X-Mailer: git-send-email 2.16.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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