• Linus Torvalds's avatar
    Merge tag 'locking-kcsan-2020-06-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip · b791d1bd
    Linus Torvalds authored
    Pull the Kernel Concurrency Sanitizer from Thomas Gleixner:
     "The Kernel Concurrency Sanitizer (KCSAN) is a dynamic race detector,
      which relies on compile-time instrumentation, and uses a
      watchpoint-based sampling approach to detect races.
    
      The feature was under development for quite some time and has already
      found legitimate bugs.
    
      Unfortunately it comes with a limitation, which was only understood
      late in the development cycle:
    
         It requires an up to date CLANG-11 compiler
    
      CLANG-11 is not yet released (scheduled for June), but it's the only
      compiler today which handles the kernel requirements and especially
      the annotations of functions to exclude them from KCSAN
      instrumentation correctly.
    
      These annotations really need to work so that low level entry code and
      especially int3 text poke handling can be completely isolated.
    
      A detailed discussion of the requirements and compiler issues can be
      found here:
    
        https://lore.kernel.org/lkml/CANpmjNMTsY_8241bS7=XAfqvZHFLrVEkv_uM4aDUWE_kh3Rvbw@mail.gmail.com/
    
      We came to the conclusion that trying to work around compiler
      limitations and bugs again would end up in a major trainwreck, so
      requiring a working compiler seemed to be the best choice.
    
      For Continous Integration purposes the compiler restriction is
      manageable and that's where most xxSAN reports come from.
    
      For a change this limitation might make GCC people actually look at
      their bugs. Some issues with CSAN in GCC are 7 years old and one has
      been 'fixed' 3 years ago with a half baken solution which 'solved' the
      reported issue but not the underlying problem.
    
      The KCSAN developers also ponder to use a GCC plugin to become
      independent, but that's not something which will show up in a few
      days.
    
      Blocking KCSAN until wide spread compiler support is available is not
      a really good alternative because the continuous growth of lockless
      optimizations in the kernel demands proper tooling support"
    
    * tag 'locking-kcsan-2020-06-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (76 commits)
      compiler_types.h, kasan: Use __SANITIZE_ADDRESS__ instead of CONFIG_KASAN to decide inlining
      compiler.h: Move function attributes to compiler_types.h
      compiler.h: Avoid nested statement expression in data_race()
      compiler.h: Remove data_race() and unnecessary checks from {READ,WRITE}_ONCE()
      kcsan: Update Documentation to change supported compilers
      kcsan: Remove 'noinline' from __no_kcsan_or_inline
      kcsan: Pass option tsan-instrument-read-before-write to Clang
      kcsan: Support distinguishing volatile accesses
      kcsan: Restrict supported compilers
      kcsan: Avoid inserting __tsan_func_entry/exit if possible
      ubsan, kcsan: Don't combine sanitizer with kcov on clang
      objtool, kcsan: Add kcsan_disable_current() and kcsan_enable_current_nowarn()
      kcsan: Add __kcsan_{enable,disable}_current() variants
      checkpatch: Warn about data_race() without comment
      kcsan: Use GFP_ATOMIC under spin lock
      Improve KCSAN documentation a bit
      kcsan: Make reporting aware of KCSAN tests
      kcsan: Fix function matching in report
      kcsan: Change data_race() to no longer require marking racing accesses
      kcsan: Move kcsan_{disable,enable}_current() to kcsan-checks.h
      ...
    b791d1bd
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