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runtime: prevent deadlock when profiling signal arrives during traceback 

Traceback routines, e.g. callers and funcentry, may call
    __go_get_backtrace_state. If a profiling signal arrives while we
    are in the critical section of __go_get_backtrace_state, it tries
    to do a traceback, which also calls __go_get_backtrace_state,
    which tries to enter the same critical section and will deadlock.
    Prevent this deadlock by setting up runtime_in_callers before
    calling __go_get_backtrace_state.
    
    Found while investigating golang/go#29448. Will add a test in the
    next CL.
    
    Updates golang/go#29448.
    
    Reviewed-on: https://go-review.googlesource.com/c/156037

From-SVN: r267590
This commit is contained in:
Ian Lance Taylor 2019-01-05 00:40:04 +00:00
parent 869fbd357e
commit f6be1179bb
3 changed files with 10 additions and 3 deletions
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2
gcc/go/gofrontend/MERGE
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@ -1,4 +1,4 @@
0e482bef69d73b9381dbc543e200a1fe57275e81
2ce291eaee427799bfcde256929dab89e0ab61eb
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.

9
libgo/runtime/go-caller.c
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@ -137,7 +137,9 @@ __go_file_line (uintptr pc, int index, String *fn, String *file, intgo *line)
runtime_memclr (&c, sizeof c);
c.index = index;
runtime_xadd (&__go_runtime_in_callers, 1);
state = __go_get_backtrace_state ();
runtime_xadd (&__go_runtime_in_callers, -1);
backtrace_pcinfo (state, pc, callback, error_callback, &c);
*fn = c.fn;
*file = c.file;
@ -169,8 +171,13 @@ syminfo_callback (void *data, uintptr_t pc __attribute__ ((unused)),
static _Bool
__go_symbol_value (uintptr pc, uintptr *val)
{
struct backtrace_state *state;
*val = 0;
backtrace_syminfo (__go_get_backtrace_state (), pc, syminfo_callback,
runtime_xadd (&__go_runtime_in_callers, 1);
state = __go_get_backtrace_state ();
runtime_xadd (&__go_runtime_in_callers, -1);
backtrace_syminfo (state, pc, syminfo_callback,
error_callback, val);
return *val != 0;
}

2
libgo/runtime/go-callers.c
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@ -202,8 +202,8 @@ runtime_callers (int32 skip, Location *locbuf, int32 m, bool keep_thunks)
data.index = 0;
data.max = m;
data.keep_thunks = keep_thunks;
state = __go_get_backtrace_state ();
runtime_xadd (&__go_runtime_in_callers, 1);
state = __go_get_backtrace_state ();
backtrace_full (state, 0, callback, error_callback, &data);
runtime_xadd (&__go_runtime_in_callers, -1);