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@xxxxxxxxxxxxxx > > 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@xxxxxxxxxxxxxx > > v3: http://lkml.kernel.org/r/20191104142745.14722-1-elver@xxxxxxxxxx > * 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@xxxxxxxxxx > * 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@xxxxxxxxxx > > 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 >
