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Bound the SIGPROF frame walk to prevent an infinite loop (4.2.2) #3

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Bound the SIGPROF frame walk to prevent an infinite loop (4.2.2) #3

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7 changes: 4 additions & 3 deletions googlecloudprofiler/__version__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@

# setup.py reads the version information from here to set package version
# Glean fork: upstream 4.1.0 + 3.12/3.13 support (vendored as 4.2.0) + the
# SIGPROF frame-walk crash fix (copy-the-chain). Patch bump over the synthetic
# 4.2.0 -- the fix is a backward-compatible bug fix. Upstream has no 4.2.x.
__version__ = '4.2.1'
# SIGPROF frame-walk crash fix (copy-the-chain, 4.2.1) + a bound on the frame
# walk to prevent an infinite loop on a torn/cyclic `previous` chain (4.2.2).
# Backward-compatible bug fixes; upstream has no 4.2.x.
__version__ = '4.2.2'
29 changes: 26 additions & 3 deletions googlecloudprofiler/src/populate_frames.cc
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Expand Up @@ -32,6 +32,14 @@ bool SafeCopy(void *dst, const void *src, size_t n) {
return got == static_cast<long>(n);
}

// Absolute cap on frames walked per SIGPROF sample. num_frames only advances for
// complete frames, so a cycle of incomplete/stale frames -- e.g. a torn
// `previous` link left by a SIGPROF landing mid frame push/pop -- would otherwise
// spin this walk forever inside the signal handler (GIL held), wedging the
// process. 4x the capture cap leaves headroom for legitimately skipped frames
// (C-stack shims, prologue frames).
static const int kMaxWalkIterations = 4 * kMaxFramesToCapture;

#if PY_VERSION_HEX >= PY_313

/**
Expand Down Expand Up @@ -92,7 +100,9 @@ int PopulateFrames(CallFrame *frames, PyThreadState *ts) {

_PyInterpreterFrame *faddr = ts->current_frame;
int num_frames = 0;
while (faddr != nullptr && num_frames < kMaxFramesToCapture) {
int steps = 0;
while (faddr != nullptr && num_frames < kMaxFramesToCapture &&
++steps <= kMaxWalkIterations) {
_PyInterpreterFrame fr;
if (!SafeCopy(&fr, faddr, sizeof(fr))) {
break; // unreadable frame: stop, keep the frames gathered so far
Expand All @@ -108,6 +118,9 @@ int PopulateFrames(CallFrame *frames, PyThreadState *ts) {
(fr.instr_ptr - _PyCode_CODE(code)) * sizeof(_Py_CODEUNIT));
num_frames++;
}
if (fr.previous == faddr) {
break; // self-referential link: stop instead of spinning
}
faddr = fr.previous;
}
return num_frames;
Expand Down Expand Up @@ -174,7 +187,9 @@ int PopulateFrames(CallFrame *frames, PyThreadState *ts) {
}

int num_frames = 0;
while (faddr != nullptr && num_frames < kMaxFramesToCapture) {
int steps = 0;
while (faddr != nullptr && num_frames < kMaxFramesToCapture &&
++steps <= kMaxWalkIterations) {
_PyInterpreterFrame fr;
if (!SafeCopy(&fr, faddr, sizeof(fr))) {
break; // unreadable frame: stop, keep the frames gathered so far
Expand All @@ -188,6 +203,9 @@ int PopulateFrames(CallFrame *frames, PyThreadState *ts) {
(fr.prev_instr - _PyCode_CODE(fr.f_code)) * sizeof(_Py_CODEUNIT));
num_frames++;
}
if (fr.previous == faddr) {
break; // self-referential link: stop instead of spinning
}
faddr = fr.previous;
}
return num_frames;
Expand Down Expand Up @@ -248,7 +266,9 @@ int PopulateFrames(CallFrame *frames, PyThreadState *ts) {
}

int num_frames = 0;
while (faddr != nullptr && num_frames < kMaxFramesToCapture) {
int steps = 0;
while (faddr != nullptr && num_frames < kMaxFramesToCapture &&
++steps <= kMaxWalkIterations) {
_PyInterpreterFrame fr;
if (!SafeCopy(&fr, faddr, sizeof(fr))) {
break; // unreadable frame: stop, keep the frames gathered so far
Expand All @@ -262,6 +282,9 @@ int PopulateFrames(CallFrame *frames, PyThreadState *ts) {
(fr.prev_instr - _PyCode_CODE(fr.f_code)) * sizeof(_Py_CODEUNIT));
num_frames++;
}
if (fr.previous == faddr) {
break; // self-referential link: stop instead of spinning
}
faddr = fr.previous;
}
return num_frames;
Expand Down