[ovs-dev] [RFC PATCH 0/8] RCU: Add blocking mode for debugging

[Gaëtan Rivet]

On Thu, Apr 22, 2021, at 17:54, Gaetan Rivet wrote:
> This series adds a compilation option that changes the behavior of the RCU
> module. Once enabled, RCU reclamation by user threads becomes blocking until
> the RCU threads has executed the scheduled callbacks.
> 
> Tools such as AddressSanitizer are useful to detect memory errors e.g. 
> user-after-free.
> Such tool can become ineffective if the RCU library is used to defer 
> memory reclamation.
> While this is the intended function of the RCU lib, nothing protects 
> developers
> from mistakes i.e. keeping references to memory scheduled for 
> reclamation accross
> quiescent periods.
> 
> Such error that should be detectable with ASAN, are made less likely to occur
> due to RCU and thus harder to fix. However, if the RCU is modified so that user
> threads are waiting on the RCU thread to execute the scheduled callbacks, they
> should be forced to happen.
> 
> Unit tests have been written that should trigger a use-after-free from ASAN.
> They are however thwarted by the RCU, until the blocking mode is enabled.
> In that case, they will always abort on the expected error.
> 
> The full test-suite can be passed with the blocking RCU mode enabled.
> An entry in the CI matrix is created for it. No error has been observed.
> 
> Gaetan Rivet (8):
>   configure: add --enable-asan option
>   tests: Add ovs-barrier unit test
>   tests: Add RCU postpone test
>   tests: Add ASAN use-after-free validation with RCU
>   ovs-thread: Fix barrier use-after-free
>   ovs-thread: Quiesce when joining pthreads
>   rcu: Remove unused perthread mutex
>   rcu: Add blocking RCU mode
> 
>  .ci/linux-build.sh                   |   8 +-
>  .github/workflows/build-and-test.yml |   7 +
>  NEWS                                 |   2 +
>  acinclude.m4                         |  31 ++++
>  configure.ac                         |   2 +
>  lib/ovs-rcu.c                        |  89 ++++++++-
>  lib/ovs-thread.c                     |  77 ++++++--
>  lib/ovs-thread.h                     |   6 +-
>  tests/atlocal.in                     |   2 +
>  tests/automake.mk                    |   2 +
>  tests/library.at                     |  49 ++++-
>  tests/test-barrier.c                 | 264 +++++++++++++++++++++++++++
>  tests/test-rcu-uaf.c                 |  98 ++++++++++
>  tests/test-rcu.c                     |  59 ++++++
>  14 files changed, 673 insertions(+), 23 deletions(-)
>  create mode 100644 tests/test-barrier.c
>  create mode 100644 tests/test-rcu-uaf.c
> 
> --
> 2.31.1
> 
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I forgot to link the CI result: https://github.com/grivet/ovs/actions/runs/774814772

-- 
Gaetan Rivet