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runtime: prevent deadlock when profiling signal arrives in stack scan

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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 The first line of this file holds the git revision number of the last
merge done from the gofrontend repository. 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 older versions of glibc when a SIGPROF signal arrives while
collecting a backtrace. */ collecting a backtrace. */
static uint32 runtime_in_callers; uint32 __go_runtime_in_callers;
/* Argument passed to callback function. */ /* Argument passed to callback function. */
@ -185,7 +185,7 @@ bool alreadyInCallers(void)
bool bool
alreadyInCallers() alreadyInCallers()
{ {
return runtime_atomicload(&runtime_in_callers) > 0; return runtime_atomicload(&__go_runtime_in_callers) > 0;
} }
/* Gather caller PC's. */ /* Gather caller PC's. */
@ -203,9 +203,9 @@ runtime_callers (int32 skip, Location *locbuf, int32 m, bool keep_thunks)
data.max = m; data.max = m;
data.keep_thunks = keep_thunks; data.keep_thunks = keep_thunks;
state = __go_get_backtrace_state (); 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); 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 /* 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 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) scanstackwithmap (void *gcw)
{ {
_Unwind_Reason_Code code; _Unwind_Reason_Code code;
runtime_xadd (&__go_runtime_in_callers, 1);
code = _Unwind_Backtrace (scanstackwithmap_callback, gcw); code = _Unwind_Backtrace (scanstackwithmap_callback, gcw);
runtime_xadd (&__go_runtime_in_callers, -1);
return code == _URC_END_OF_STACK; 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) bool probestackmaps(void)
__asm__("runtime.probestackmaps"); __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;