[compiler-rt] r281969 - tsan: make CHECK more robust

Tue Sep 20 23:33:50 PDT 2016

On Tue, Sep 20, 2016 at 10:57 PM, Kostya Serebryany <kcc at google.com> wrote:
> Then make it have a fake one.
> These #ifs cost us very much in the long run.

What is that cost? I can't remember any cases where they added cost.

I remember cases when Go runtime become broken (don't built/link). But
in all these cases the right answer is to exclude more code from Go
build, rather than to pull in more code. Providing fake stubs would
cause bloat with unnecessary functions, which now build successfully
so nobody cares.

If we introduce fake cur_thread() for Go, _it_ has good chances to add
visible cost due to additional bugs. Looking at existing usages of
cur_thread(), accidentally using a fake cur_thread() for Go would be
very wrong. For example, calling HACKY_CALL(trace_switch) in Go would
cause operating on a wrong ThreadState -- we don't need the fake one,
we need the real one. For internal deadlock detector using a global
fake ThreadState would cause bad races on the object.

I don't see how it is better and what is the current cost of #if's.

> On Tue, Sep 20, 2016 at 1:56 PM, Dmitry Vyukov <dvyukov at google.com> wrote:
>>
>> No, because Go does not have cur_thread().
>>
>> On Tue, Sep 20, 2016 at 11:54 PM, Kostya Serebryany <kcc at google.com>
>> wrote:
>> > Please, can we have if() instead of #if?
>> >
>> > On Tue, Sep 20, 2016 at 6:28 AM, Dmitry Vyukov via llvm-commits
>> > <llvm-commits at lists.llvm.org> wrote:
>> >>
>> >> Author: dvyukov
>> >> Date: Tue Sep 20 08:28:20 2016
>> >> New Revision: 281969
>> >>
>> >> URL: http://llvm.org/viewvc/llvm-project?rev=281969&view=rev
>> >> Log:
>> >> tsan: make CHECK more robust
>> >>
>> >> Enable more ignores when we start crashing.
>> >> Unwind in CHECK SIGSEGVs if happens early:
>> >>
>> >> FATAL: ThreadSanitizer CHECK failed:
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_platform_posix.cc:105
>> >> "((beg)) <=
>> >> ((end))" (0x8000000000, 0x4000000000)
>> >> Program received signal SIGSEGV, Segmentation fault.
>> >> __tsan::MetaMap::GetAndLock (this=0x1337c88
>> >> <__tsan::ctx_placeholder+8>,
>> >> thr=thr at entry=0x7ffff7f91800, pc=pc at entry=4639488,
>> >> addr=addr at entry=140737339086992, write_lock=write_lock at entry=true,
>> >>     create=create at entry=true) at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_sync.cc:208
>> >> 208       u32 idx0 = *meta;
>> >> (gdb) bt
>> >> #0  __tsan::MetaMap::GetAndLock (this=0x1337c88
>> >> <__tsan::ctx_placeholder+8>, thr=thr at entry=0x7ffff7f91800,
>> >> pc=pc at entry=4639488, addr=addr at entry=140737339086992,
>> >> write_lock=write_lock at entry=true,
>> >>     create=create at entry=true) at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_sync.cc:208
>> >> #1  0x00000000004a965f in __tsan::MetaMap::GetOrCreateAndLock
>> >> (this=<optimized out>, thr=thr at entry=0x7ffff7f91800,
>> >> pc=pc at entry=4639488,
>> >> addr=addr at entry=140737339086992, write_lock=write_lock at entry=true)
>> >>     at ../projects/compiler-rt/lib/tsan/rtl/tsan_sync.cc:198
>> >> #2  0x00000000004a162a in __tsan::Release (thr=0x7ffff7f91800,
>> >> pc=pc at entry=4639488, addr=addr at entry=140737339086992) at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_rtl_mutex.cc:395
>> >> #3  0x000000000046cc40 in __interceptor_pthread_once (o=0x7ffff71a5890
>> >> <once_regsizes>, f=0x7ffff6f9d9c0 <init_dwarf_reg_size_table>) at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc:1334
>> >> #4  0x00007ffff6f9fe86 in __gthread_once (__func=0x7ffff6f9d9c0
>> >> <init_dwarf_reg_size_table>, __once=0x7ffff71a5890 <once_regsizes>) at
>> >> ./gthr-default.h:699
>> >> #5  uw_init_context_1 (context=context at entry=0x7fffffffd6d0,
>> >> outer_cfa=outer_cfa at entry=0x7fffffffd980, outer_ra=0x437d13
>> >> <__sanitizer::BufferedStackTrace::SlowUnwindStack(unsigned long,
>> >> unsigned
>> >> int)+67>)
>> >>     at ../../../src/libgcc/unwind-dw2.c:1572
>> >> #6  0x00007ffff6fa06a8 in _Unwind_Backtrace (trace=0x437c30
>> >> <__sanitizer::Unwind_Trace(_Unwind_Context*, void*)>,
>> >> trace_argument=0x7fffffffd980) at ../../../src/libgcc/unwind.inc:283
>> >> #7  0x0000000000437d13 in
>> >> __sanitizer::BufferedStackTrace::SlowUnwindStack
>> >> (this=0x7ffff6103208, pc=pc at entry=4863574,
>> >> max_depth=max_depth at entry=256)
>> >>     at
>> >>
>> >> ../projects/compiler-rt/lib/sanitizer_common/sanitizer_unwind_linux_libcdep.cc:125
>> >> #8  0x0000000000434f4a in __sanitizer::BufferedStackTrace::Unwind
>> >> (this=this at entry=0x7ffff6103208, max_depth=max_depth at entry=256,
>> >> pc=pc at entry=4863574, bp=bp at entry=0, context=context at entry=0x0,
>> >>     stack_top=stack_top at entry=0, stack_bottom=stack_bottom at entry=0,
>> >> request_fast_unwind=request_fast_unwind at entry=false) at
>> >>
>> >> ../projects/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc:76
>> >> #9  0x00000000004a36b3 in PrintCurrentStackSlow (pc=4863574) at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_rtl_report.cc:696
>> >> #10 __tsan::TsanCheckFailed (file=<optimized out>, line=<optimized
>> >> out>,
>> >> cond=<optimized out>, v1=<optimized out>, v2=<optimized out>) at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_rtl_report.cc:44
>> >> #11 0x000000000042dfd6 in __sanitizer::CheckFailed
>> >> (file=file at entry=0x4b9fd0
>> >> "../projects/compiler-rt/lib/tsan/rtl/tsan_platform_posix.cc",
>> >> line=line at entry=105,
>> >>     cond=cond at entry=0x4ba049 "((beg)) <= ((end))",
>> >> v1=v1 at entry=549755813888, v2=v2 at entry=274877906944) at
>> >>
>> >> ../projects/compiler-rt/lib/sanitizer_common/sanitizer_termination.cc:79
>> >> #12 0x00000000004aa36c in ProtectRange (end=274877906944,
>> >> beg=549755813888) at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_platform_posix.cc:105
>> >> #13 __tsan::CheckAndProtect () at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_platform_posix.cc:133
>> >> #14 0x00000000004a9e95 in __tsan::InitializePlatform () at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_platform_linux.cc:280
>> >> #15 0x0000000000497e73 in __tsan::Initialize (thr=0x7ffff7f91800) at
>> >> ../projects/compiler-rt/lib/tsan/rtl/tsan_rtl.cc:343
>> >> #16 0x00007ffff7dea25a in _dl_init (main_map=0x7ffff7ffe1c8, argc=1,
>> >> argv=0x7fffffffdb88, env=0x7fffffffdb98) at dl-init.c:111
>> >> #17 0x00007ffff7ddb30a in _dl_start_user () at rtld.c:871
>> >>
>> >>
>> >> Modified:
>> >>     compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_report.cc
>> >>
>> >> Modified: compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_report.cc
>> >> URL:
>> >>
>> >> http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_report.cc?rev=281969&r1=281968&r2=281969&view=diff
>> >>
>> >>
>> >> ==============================================================================
>> >> --- compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_report.cc (original)
>> >> +++ compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_report.cc Tue Sep 20
>> >> 08:28:20
>> >> 2016
>> >> @@ -38,6 +38,10 @@ void TsanCheckFailed(const char *file, i
>> >>    // on the other hand there is no sense in processing interceptors
>> >>    // since we are going to die soon.
>> >>    ScopedIgnoreInterceptors ignore;
>> >> +#ifndef SANITIZER_GO
>> >> +  cur_thread()->ignore_sync++;
>> >> +  cur_thread()->ignore_reads_and_writes++;
>> >> +#endif
>> >>    Printf("FATAL: ThreadSanitizer CHECK failed: "
>> >>           "%s:%d \"%s\" (0x%zx, 0x%zx)\n",
>> >>           file, line, cond, (uptr)v1, (uptr)v2);
>> >>
>> >>
>> >> _______________________________________________
>> >> llvm-commits mailing list
>> >> llvm-commits at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>> >
>> >
>
>