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Date: Tue, 26 Sep 2017 06:18:34 +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/lockdep v3 00/14] lockdep: Support deadlock detection for recursive read locks Hi Ingo and Peter, This is V3 for recursive read lock support in lockdep. Changes since V2: * Add one revert patch for commit d82fed752942 ("locking/lockdep/selftests: Fix mixed read-write ABBA tests"), since we could handle recursive read lock correctly, so we don't need to fudge the test anymore. * More document and print-message changes for redefining LOCK*_STATE*. * Rewrite some commit logs to improve the explanation of the idea. V1: https://marc.info/?l=linux-kernel&m=150393341825453 V2: https://marc.info/?l=linux-kernel&m=150468649417950 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 tip tree: a35205980288 ("Merge branch 'WIP.x86/fpu'") , and I also put it at: git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git arr-rfc-v3 The whole series consists of 14 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"), This series passed all the lockdep selftest cases(including those I introduce). Will play more other tests, and in the meanwhile hope to hear your thoughts about this. Test and comments are welcome! Regards, Boqun
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