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runtime: prevent deadlock when profiling signal arrives in stack scan 

Precise stack scan needs to unwind the stack. When it is
    unwinding the stack, if a profiling signal arrives, which also
    does a traceback, it may deadlock in dl_iterate_phdr. Prevent
    this deadlock by setting up runtime_in_callers before traceback.
    
    Reviewed-on: https://go-review.googlesource.com/c/155766

From-SVN: r267457
This commit is contained in:
Ian Lance Taylor 2018-12-29 00:07:06 +00:00
parent 50bec22834
commit e20bfbd18e
4 changed files with 13 additions and 5 deletions
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2
gcc/go/gofrontend/MERGE
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@ -1,4 +1,4 @@
d9a30434440469c640a120fe7132057f5644d38c
0e482bef69d73b9381dbc543e200a1fe57275e81
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.

8
libgo/runtime/go-callers.c
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@ -16,7 +16,7 @@
older versions of glibc when a SIGPROF signal arrives while
collecting a backtrace. */
static uint32 runtime_in_callers;
uint32 __go_runtime_in_callers;
/* Argument passed to callback function. */
@ -185,7 +185,7 @@ bool alreadyInCallers(void)
bool
alreadyInCallers()
{
return runtime_atomicload(&runtime_in_callers) > 0;
return runtime_atomicload(&__go_runtime_in_callers) > 0;
}
/* Gather caller PC's. */
@ -203,9 +203,9 @@ runtime_callers (int32 skip, Location *locbuf, int32 m, bool keep_thunks)
data.max = m;
data.keep_thunks = keep_thunks;
state = __go_get_backtrace_state ();
runtime_xadd (&runtime_in_callers, 1);
runtime_xadd (&__go_runtime_in_callers, 1);
backtrace_full (state, 0, callback, error_callback, &data);
runtime_xadd (&runtime_in_callers, -1);
runtime_xadd (&__go_runtime_in_callers, -1);
/* For some reason GCC sometimes loses the name of a thunk function
at the top of the stack. If we are skipping thunks, skip that

2
libgo/runtime/go-unwind.c
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@ -792,7 +792,9 @@ bool
scanstackwithmap (void *gcw)
{
_Unwind_Reason_Code code;
runtime_xadd (&__go_runtime_in_callers, 1);
code = _Unwind_Backtrace (scanstackwithmap_callback, gcw);
runtime_xadd (&__go_runtime_in_callers, -1);
return code == _URC_END_OF_STACK;
}

6
libgo/runtime/runtime.h
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@ -515,3 +515,9 @@ bool runtime_usestackmaps;
bool probestackmaps(void)
__asm__("runtime.probestackmaps");
// This is set to non-zero when calling backtrace_full. This is used
// to avoid getting hanging on a recursive lock in dl_iterate_phdr on
// older versions of glibc when a SIGPROF signal arrives while
// collecting a backtrace.
extern uint32 __go_runtime_in_callers;