From 183a40db6def2780478053b3cd14f3f5c355d999 Mon Sep 17 00:00:00 2001 From: Nick Ripley Date: Tue, 2 Jul 2024 12:53:36 -0400 Subject: [PATCH] runtime: avoid multiple records with identical stacks from MutexProfile MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When using frame pointer unwinding, we defer frame skipping and inline expansion for call stacks until profile reporting time. We can end up with records which have different stacks if no frames are skipped, but identical stacks once skipping is taken into account. Returning multiple records with the same stack (but different values) has broken programs which rely on the records already being fully aggregated by call stack when returned from runtime.MutexProfile. This CL addresses the problem by handling skipping at recording time. We do full inline expansion to correctly skip the desired number of frames when recording the call stack, and then handle the rest of inline expansion when reporting the profile. The regression test in this CL is adapted from the reproducer in https://github.com/grafana/pyroscope-go/issues/103, authored by Tolya Korniltsev. Fixes #67548 Co-Authored-By: Tolya Korniltsev Change-Id: I6a42ce612377f235b2c8c0cec9ba8e9331224b84 Reviewed-on: https://go-review.googlesource.com/c/go/+/595966 LUCI-TryBot-Result: Go LUCI Reviewed-by: Carlos Amedee Reviewed-by: Cherry Mui Auto-Submit: Carlos Amedee Reviewed-by: Felix Geisendörfer --- src/runtime/mprof.go | 105 ++++++++++++++++++++++++++++---- src/runtime/pprof/pprof.go | 23 ++++++- src/runtime/pprof/pprof_test.go | 78 ++++++++++++++++++++++++ 3 files changed, 192 insertions(+), 14 deletions(-) diff --git a/src/runtime/mprof.go b/src/runtime/mprof.go index b4fe0e5549c7c..e5620aec11dfd 100644 --- a/src/runtime/mprof.go +++ b/src/runtime/mprof.go @@ -9,6 +9,7 @@ package runtime import ( "internal/abi" + "internal/goarch" "internal/profilerecord" "internal/runtime/atomic" "runtime/internal/sys" @@ -542,16 +543,14 @@ func saveblockevent(cycles, rate int64, skip int, which bucketType) { gp := getg() mp := acquirem() // we must not be preempted while accessing profstack - nstk := 1 + var nstk int if tracefpunwindoff() || gp.m.hasCgoOnStack() { - mp.profStack[0] = logicalStackSentinel if gp.m.curg == nil || gp.m.curg == gp { - nstk = callers(skip, mp.profStack[1:]) + nstk = callers(skip, mp.profStack) } else { - nstk = gcallers(gp.m.curg, skip, mp.profStack[1:]) + nstk = gcallers(gp.m.curg, skip, mp.profStack) } } else { - mp.profStack[0] = uintptr(skip) if gp.m.curg == nil || gp.m.curg == gp { if skip > 0 { // We skip one fewer frame than the provided value for frame @@ -559,12 +558,12 @@ func saveblockevent(cycles, rate int64, skip int, which bucketType) { // frame, whereas the saved frame pointer will give us the // caller's return address first (so, not including // saveblockevent) - mp.profStack[0] -= 1 + skip -= 1 } - nstk += fpTracebackPCs(unsafe.Pointer(getfp()), mp.profStack[1:]) + nstk = fpTracebackPartialExpand(skip, unsafe.Pointer(getfp()), mp.profStack) } else { - mp.profStack[1] = gp.m.curg.sched.pc - nstk += 1 + fpTracebackPCs(unsafe.Pointer(gp.m.curg.sched.bp), mp.profStack[2:]) + mp.profStack[0] = gp.m.curg.sched.pc + nstk = 1 + fpTracebackPartialExpand(skip, unsafe.Pointer(gp.m.curg.sched.bp), mp.profStack[1:]) } } @@ -572,6 +571,52 @@ func saveblockevent(cycles, rate int64, skip int, which bucketType) { releasem(mp) } +// fpTracebackPartialExpand records a call stack obtained starting from fp. +// This function will skip the given number of frames, properly accounting for +// inlining, and save remaining frames as "physical" return addresses. The +// consumer should later use CallersFrames or similar to expand inline frames. +func fpTracebackPartialExpand(skip int, fp unsafe.Pointer, pcBuf []uintptr) int { + var n int + lastFuncID := abi.FuncIDNormal + skipOrAdd := func(retPC uintptr) bool { + if skip > 0 { + skip-- + } else if n < len(pcBuf) { + pcBuf[n] = retPC + n++ + } + return n < len(pcBuf) + } + for n < len(pcBuf) && fp != nil { + // return addr sits one word above the frame pointer + pc := *(*uintptr)(unsafe.Pointer(uintptr(fp) + goarch.PtrSize)) + + if skip > 0 { + callPC := pc - 1 + fi := findfunc(callPC) + u, uf := newInlineUnwinder(fi, callPC) + for ; uf.valid(); uf = u.next(uf) { + sf := u.srcFunc(uf) + if sf.funcID == abi.FuncIDWrapper && elideWrapperCalling(lastFuncID) { + // ignore wrappers + } else if more := skipOrAdd(uf.pc + 1); !more { + return n + } + lastFuncID = sf.funcID + } + } else { + // We've skipped the desired number of frames, so no need + // to perform further inline expansion now. + pcBuf[n] = pc + n++ + } + + // follow the frame pointer to the next one + fp = unsafe.Pointer(*(*uintptr)(fp)) + } + return n +} + // lockTimer assists with profiling contention on runtime-internal locks. // // There are several steps between the time that an M experiences contention and @@ -1075,10 +1120,34 @@ type BlockProfileRecord struct { // the [testing] package's -test.blockprofile flag instead // of calling BlockProfile directly. func BlockProfile(p []BlockProfileRecord) (n int, ok bool) { - return blockProfileInternal(len(p), func(r profilerecord.BlockProfileRecord) { + n, ok = blockProfileInternal(len(p), func(r profilerecord.BlockProfileRecord) { copyBlockProfileRecord(&p[0], r) p = p[1:] }) + if !ok { + return + } + expandFrames(p[:n]) + return +} + +func expandFrames(p []BlockProfileRecord) { + expandedStack := makeProfStack() + for i := range p { + cf := CallersFrames(p[i].Stack()) + j := 0 + for ; j < len(expandedStack); j++ { + f, more := cf.Next() + // f.PC is a "call PC", but later consumers will expect + // "return PCs" + expandedStack[i] = f.PC + 1 + if !more { + break + } + } + k := copy(p[i].Stack0[:], expandedStack[:j]) + clear(p[i].Stack0[k:]) + } } // blockProfileInternal returns the number of records n in the profile. If there @@ -1111,6 +1180,9 @@ func blockProfileInternal(size int, copyFn func(profilerecord.BlockProfileRecord return } +// copyBlockProfileRecord copies the sample values and call stack from src to dst. +// The call stack is copied as-is. The caller is responsible for handling inline +// expansion, needed when the call stack was collected with frame pointer unwinding. func copyBlockProfileRecord(dst *BlockProfileRecord, src profilerecord.BlockProfileRecord) { dst.Count = src.Count dst.Cycles = src.Cycles @@ -1123,7 +1195,11 @@ func copyBlockProfileRecord(dst *BlockProfileRecord, src profilerecord.BlockProf if asanenabled { asanwrite(unsafe.Pointer(&dst.Stack0[0]), unsafe.Sizeof(dst.Stack0)) } - i := fpunwindExpand(dst.Stack0[:], src.Stack) + // We just copy the stack here without inline expansion + // (needed if frame pointer unwinding is used) + // since this function is called under the profile lock, + // and doing something that might allocate can violate lock ordering. + i := copy(dst.Stack0[:], src.Stack) clear(dst.Stack0[i:]) } @@ -1142,10 +1218,15 @@ func pprof_blockProfileInternal(p []profilerecord.BlockProfileRecord) (n int, ok // Most clients should use the [runtime/pprof] package // instead of calling MutexProfile directly. func MutexProfile(p []BlockProfileRecord) (n int, ok bool) { - return mutexProfileInternal(len(p), func(r profilerecord.BlockProfileRecord) { + n, ok = mutexProfileInternal(len(p), func(r profilerecord.BlockProfileRecord) { copyBlockProfileRecord(&p[0], r) p = p[1:] }) + if !ok { + return + } + expandFrames(p[:n]) + return } // mutexProfileInternal returns the number of records n in the profile. If there diff --git a/src/runtime/pprof/pprof.go b/src/runtime/pprof/pprof.go index d3af5bba914ec..4b7a9f63c6500 100644 --- a/src/runtime/pprof/pprof.go +++ b/src/runtime/pprof/pprof.go @@ -404,6 +404,25 @@ type countProfile interface { Label(i int) *labelMap } +// expandInlinedFrames copies the call stack from pcs into dst, expanding any +// PCs corresponding to inlined calls into the corresponding PCs for the inlined +// functions. Returns the number of frames copied to dst. +func expandInlinedFrames(dst, pcs []uintptr) int { + cf := runtime.CallersFrames(pcs) + var n int + for n < len(dst) { + f, more := cf.Next() + // f.PC is a "call PC", but later consumers will expect + // "return PCs" + dst[n] = f.PC + 1 + n++ + if !more { + break + } + } + return n +} + // printCountCycleProfile outputs block profile records (for block or mutex profiles) // as the pprof-proto format output. Translations from cycle count to time duration // are done because The proto expects count and time (nanoseconds) instead of count @@ -426,7 +445,7 @@ func printCountCycleProfile(w io.Writer, countName, cycleName string, records [] values[1] = int64(float64(r.Cycles) / cpuGHz) // For count profiles, all stack addresses are // return PCs, which is what appendLocsForStack expects. - n := pprof_fpunwindExpand(expandedStack[:], r.Stack) + n := expandInlinedFrames(expandedStack, r.Stack) locs = b.appendLocsForStack(locs[:0], expandedStack[:n]) b.pbSample(values, locs, nil) } @@ -935,7 +954,7 @@ func writeProfileInternal(w io.Writer, debug int, name string, runtimeProfile fu for i := range p { r := &p[i] fmt.Fprintf(w, "%v %v @", r.Cycles, r.Count) - n := pprof_fpunwindExpand(expandedStack, r.Stack) + n := expandInlinedFrames(expandedStack, r.Stack) stack := expandedStack[:n] for _, pc := range stack { fmt.Fprintf(w, " %#x", pc) diff --git a/src/runtime/pprof/pprof_test.go b/src/runtime/pprof/pprof_test.go index 09abbb31ae6cc..bd11914544fbc 100644 --- a/src/runtime/pprof/pprof_test.go +++ b/src/runtime/pprof/pprof_test.go @@ -2578,3 +2578,81 @@ func produceProfileEvents(t *testing.T, depth int) { runtime.GC() goroutineDeep(t, depth-4) // -4 for produceProfileEvents, **, chanrecv1, chanrev, gopark } + +func TestMutexBlockFullAggregation(t *testing.T) { + // This regression test is adapted from + // https://github.com/grafana/pyroscope-go/issues/103, + // authored by Tolya Korniltsev + + var m sync.Mutex + + prev := runtime.SetMutexProfileFraction(-1) + defer runtime.SetMutexProfileFraction(prev) + + const fraction = 1 + const iters = 100 + const workers = 2 + + runtime.SetMutexProfileFraction(fraction) + runtime.SetBlockProfileRate(1) + defer runtime.SetBlockProfileRate(0) + + wg := sync.WaitGroup{} + wg.Add(workers) + for j := 0; j < workers; j++ { + go func() { + for i := 0; i < iters; i++ { + m.Lock() + // Wait at least 1 millisecond to pass the + // starvation threshold for the mutex + time.Sleep(time.Millisecond) + m.Unlock() + } + wg.Done() + }() + } + wg.Wait() + + assertNoDuplicates := func(name string, collect func([]runtime.BlockProfileRecord) (int, bool)) { + var p []runtime.BlockProfileRecord + n, ok := collect(nil) + for { + p = make([]runtime.BlockProfileRecord, n+50) + n, ok = collect(p) + if ok { + p = p[:n] + break + } + } + seen := make(map[string]struct{}) + for _, r := range p { + cf := runtime.CallersFrames(r.Stack()) + var stack strings.Builder + for { + f, more := cf.Next() + stack.WriteString(f.Func.Name()) + if !more { + break + } + stack.WriteByte('\n') + } + s := stack.String() + if !strings.Contains(s, "TestMutexBlockFullAggregation") { + continue + } + if _, ok := seen[s]; ok { + t.Errorf("saw duplicate entry in %s profile with stack:\n%s", name, s) + } + seen[s] = struct{}{} + } + if len(seen) == 0 { + t.Errorf("did not see any samples in %s profile for this test", name) + } + } + t.Run("mutex", func(t *testing.T) { + assertNoDuplicates("mutex", runtime.MutexProfile) + }) + t.Run("block", func(t *testing.T) { + assertNoDuplicates("block", runtime.BlockProfile) + }) +}