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Date: Thu, 14 Nov 2019 11:50:46 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Marco Elver <elver@...gle.com>
Cc: akiyks@...il.com, stern@...land.harvard.edu, glider@...gle.com,
parri.andrea@...il.com, andreyknvl@...gle.com, luto@...nel.org,
ard.biesheuvel@...aro.org, arnd@...db.de, boqun.feng@...il.com,
bp@...en8.de, dja@...ens.net, dlustig@...dia.com,
dave.hansen@...ux.intel.com, dhowells@...hat.com,
dvyukov@...gle.com, hpa@...or.com, mingo@...hat.com,
j.alglave@....ac.uk, joel@...lfernandes.org, corbet@....net,
jpoimboe@...hat.com, luc.maranget@...ia.fr, mark.rutland@....com,
npiggin@...il.com, peterz@...radead.org, tglx@...utronix.de,
will@...nel.org, edumazet@...gle.com, kasan-dev@...glegroups.com,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
linux-efi@...r.kernel.org, linux-kbuild@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH v4 00/10] Add Kernel Concurrency Sanitizer (KCSAN)
On Thu, Nov 14, 2019 at 07:02:53PM +0100, Marco Elver wrote:
> This is the patch-series for the Kernel Concurrency Sanitizer (KCSAN).
> KCSAN is a sampling watchpoint-based *data race detector*. More details
> are included in **Documentation/dev-tools/kcsan.rst**. This patch-series
> only enables KCSAN for x86, but we expect adding support for other
> architectures is relatively straightforward (we are aware of
> experimental ARM64 and POWER support).
>
> To gather early feedback, we announced KCSAN back in September, and have
> integrated the feedback where possible:
> http://lkml.kernel.org/r/CANpmjNPJ_bHjfLZCAPV23AXFfiPiyXXqqu72n6TgWzb2Gnu1eA@mail.gmail.com
>
> The current list of known upstream fixes for data races found by KCSAN
> can be found here:
> https://github.com/google/ktsan/wiki/KCSAN#upstream-fixes-of-data-races-found-by-kcsan
>
> We want to point out and acknowledge the work surrounding the LKMM,
> including several articles that motivate why data races are dangerous
> [1, 2], justifying a data race detector such as KCSAN.
>
> [1] https://lwn.net/Articles/793253/
> [2] https://lwn.net/Articles/799218/
I queued this and ran a quick rcutorture on it, which completed
successfully with quite a few reports.
Thanx, Paul
> Race conditions vs. data races
> ------------------------------
>
> Race conditions are logic bugs, where unexpected interleaving of racing
> concurrent operations result in an erroneous state.
>
> Data races on the other hand are defined at the *memory model/language
> level*. Many data races are also harmful race conditions, which a tool
> like KCSAN reports! However, not all data races are race conditions and
> vice-versa. KCSAN's intent is to report data races according to the
> LKMM. A data race detector can only work at the memory model/language
> level.
>
> Deeper analysis, to find high-level race conditions only, requires
> conveying the intended kernel logic to a tool. This requires (1) the
> developer writing a specification or model of their code, and then (2)
> the tool verifying that the implementation matches. This has been done
> for small bits of code using model checkers and other formal methods,
> but does not scale to the level of what can be covered with a dynamic
> analysis based data race detector such as KCSAN.
>
> For reasons outlined in [1, 2], data races can be much more subtle, but
> can cause no less harm than high-level race conditions.
>
> Changelog
> ---------
> v4:
> * Major changes:
> - Optimizations resulting in performance improvement of 33% (on
> microbenchmark).
> - Deal with nested interrupts for atomic_next.
> - Simplify report.c (removing double-locking as well), in preparation
> for KCSAN_REPORT_VALUE_CHANGE_ONLY.
> - Add patch to introduce "data_race(expr)" macro.
> - Introduce KCSAN_REPORT_VALUE_CHANGE_ONLY option for further filtering of data
> races: if a conflicting write was observed via a watchpoint, only report the
> data race if a value change was observed as well. The option will be enabled
> by default on syzbot. (rcu-functions will be excluded from this filter at
> request of Paul McKenney.) Context:
> http://lkml.kernel.org/r/CANpmjNOepvb6+zJmDePxj21n2rctM4Sp4rJ66x_J-L1UmNK54A@mail.gmail.com
>
> v3: http://lkml.kernel.org/r/20191104142745.14722-1-elver@google.com
> * Major changes:
> - Add microbenchmark.
> - Add instruction watchpoint skip randomization.
> - Refactor API and core runtime fast-path and slow-path. Compared to
> the previous version, with a default config and benchmarked using the
> added microbenchmark, this version is 3.8x faster.
> - Make __tsan_unaligned __alias of generic accesses.
> - Rename kcsan_{begin,end}_atomic ->
> kcsan_{nestable,flat}_atomic_{begin,end}
> - For filter list in debugfs.c use kmalloc+krealloc instead of
> kvmalloc.
> - Split Documentation into separate patch.
>
> v2: http://lkml.kernel.org/r/20191017141305.146193-1-elver@google.com
> * Major changes:
> - Replace kcsan_check_access(.., {true, false}) with
> kcsan_check_{read,write}.
> - Change atomic-instrumented.h to use __atomic_check_{read,write}.
> - Use common struct kcsan_ctx in task_struct and for per-CPU interrupt
> contexts.
>
> v1: http://lkml.kernel.org/r/20191016083959.186860-1-elver@google.com
>
> Marco Elver (10):
> kcsan: Add Kernel Concurrency Sanitizer infrastructure
> include/linux/compiler.h: Introduce data_race(expr) macro
> kcsan: Add Documentation entry in dev-tools
> objtool, kcsan: Add KCSAN runtime functions to whitelist
> build, kcsan: Add KCSAN build exceptions
> seqlock, kcsan: Add annotations for KCSAN
> seqlock: Require WRITE_ONCE surrounding raw_seqcount_barrier
> asm-generic, kcsan: Add KCSAN instrumentation for bitops
> locking/atomics, kcsan: Add KCSAN instrumentation
> x86, kcsan: Enable KCSAN for x86
>
> Documentation/dev-tools/index.rst | 1 +
> Documentation/dev-tools/kcsan.rst | 256 +++++++++
> MAINTAINERS | 11 +
> Makefile | 3 +-
> arch/x86/Kconfig | 1 +
> arch/x86/boot/Makefile | 2 +
> arch/x86/boot/compressed/Makefile | 2 +
> arch/x86/entry/vdso/Makefile | 3 +
> arch/x86/include/asm/bitops.h | 6 +-
> arch/x86/kernel/Makefile | 4 +
> arch/x86/kernel/cpu/Makefile | 3 +
> arch/x86/lib/Makefile | 4 +
> arch/x86/mm/Makefile | 4 +
> arch/x86/purgatory/Makefile | 2 +
> arch/x86/realmode/Makefile | 3 +
> arch/x86/realmode/rm/Makefile | 3 +
> drivers/firmware/efi/libstub/Makefile | 2 +
> include/asm-generic/atomic-instrumented.h | 393 +++++++-------
> include/asm-generic/bitops-instrumented.h | 18 +
> include/linux/compiler-clang.h | 9 +
> include/linux/compiler-gcc.h | 7 +
> include/linux/compiler.h | 57 +-
> include/linux/kcsan-checks.h | 97 ++++
> include/linux/kcsan.h | 115 ++++
> include/linux/sched.h | 4 +
> include/linux/seqlock.h | 51 +-
> init/init_task.c | 8 +
> init/main.c | 2 +
> kernel/Makefile | 6 +
> kernel/kcsan/Makefile | 11 +
> kernel/kcsan/atomic.h | 27 +
> kernel/kcsan/core.c | 626 ++++++++++++++++++++++
> kernel/kcsan/debugfs.c | 275 ++++++++++
> kernel/kcsan/encoding.h | 94 ++++
> kernel/kcsan/kcsan.h | 108 ++++
> kernel/kcsan/report.c | 320 +++++++++++
> kernel/kcsan/test.c | 121 +++++
> kernel/sched/Makefile | 6 +
> lib/Kconfig.debug | 2 +
> lib/Kconfig.kcsan | 118 ++++
> lib/Makefile | 3 +
> mm/Makefile | 8 +
> scripts/Makefile.kcsan | 6 +
> scripts/Makefile.lib | 10 +
> scripts/atomic/gen-atomic-instrumented.sh | 17 +-
> tools/objtool/check.c | 18 +
> 46 files changed, 2641 insertions(+), 206 deletions(-)
> create mode 100644 Documentation/dev-tools/kcsan.rst
> create mode 100644 include/linux/kcsan-checks.h
> create mode 100644 include/linux/kcsan.h
> create mode 100644 kernel/kcsan/Makefile
> create mode 100644 kernel/kcsan/atomic.h
> create mode 100644 kernel/kcsan/core.c
> create mode 100644 kernel/kcsan/debugfs.c
> create mode 100644 kernel/kcsan/encoding.h
> create mode 100644 kernel/kcsan/kcsan.h
> create mode 100644 kernel/kcsan/report.c
> create mode 100644 kernel/kcsan/test.c
> create mode 100644 lib/Kconfig.kcsan
> create mode 100644 scripts/Makefile.kcsan
>
> --
> 2.24.0.rc1.363.gb1bccd3e3d-goog
>
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