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author | Vladimir Stefanovic <vladimir.stefanovic@imgtec.com> | 2017-05-04 16:45:29 +0200 |
---|---|---|
committer | Cherry Zhang <cherryyz@google.com> | 2017-07-26 13:29:59 +0000 |
commit | 835dfef939879b284d4c0f4e1726491f27e4f1ee (patch) | |
tree | d163be310654d08362c9f7b620bf8e4c46d0dca2 | |
parent | df91b8044dbe790c69c16058330f545be069cc1f (diff) | |
download | go-835dfef939879b284d4c0f4e1726491f27e4f1ee.tar.gz go-835dfef939879b284d4c0f4e1726491f27e4f1ee.zip |
runtime/pprof: prevent a deadlock that SIGPROF might create on mips{,le}
64bit atomics on mips/mipsle are implemented using spinlocks. If SIGPROF
is received while the program is in the critical section, it will try to
write the sample using the same spinlock, creating a deadloop.
Prevent it by creating a counter of SIGPROFs during atomic64 and
postpone writing the sample(s) until called from elsewhere, with
pc set to _LostSIGPROFDuringAtomic64.
Added a test case, per Cherry's suggestion. Works around #20146.
Change-Id: Icff504180bae4ee83d78b19c0d9d6a80097087f9
Reviewed-on: https://go-review.googlesource.com/42652
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
-rw-r--r-- | src/runtime/cpuprof.go | 9 | ||||
-rw-r--r-- | src/runtime/pprof/pprof_test.go | 31 | ||||
-rw-r--r-- | src/runtime/proc.go | 31 |
3 files changed, 67 insertions, 4 deletions
diff --git a/src/runtime/cpuprof.go b/src/runtime/cpuprof.go index c761e440b6..fb841a9f3d 100644 --- a/src/runtime/cpuprof.go +++ b/src/runtime/cpuprof.go @@ -163,6 +163,15 @@ func (p *cpuProfile) addExtra() { } } +func (p *cpuProfile) addLostAtomic64(count uint64) { + hdr := [1]uint64{count} + lostStk := [2]uintptr{ + funcPC(_LostSIGPROFDuringAtomic64) + sys.PCQuantum, + funcPC(_System) + sys.PCQuantum, + } + cpuprof.log.write(nil, 0, hdr[:], lostStk[:]) +} + // CPUProfile panics. // It formerly provided raw access to chunks of // a pprof-format profile generated by the runtime. diff --git a/src/runtime/pprof/pprof_test.go b/src/runtime/pprof/pprof_test.go index 22fea0a52f..992d2abb6a 100644 --- a/src/runtime/pprof/pprof_test.go +++ b/src/runtime/pprof/pprof_test.go @@ -12,6 +12,7 @@ import ( "fmt" "internal/testenv" "io" + "io/ioutil" "math/big" "os" "os/exec" @@ -20,6 +21,7 @@ import ( "runtime/pprof/internal/profile" "strings" "sync" + "sync/atomic" "testing" "time" ) @@ -713,3 +715,32 @@ func TestCPUProfileLabel(t *testing.T) { }) }) } + +// Check that there is no deadlock when the program receives SIGPROF while in +// 64bit atomics' critical section. Used to happen on mips{,le}. See #20146. +func TestAtomicLoadStore64(t *testing.T) { + f, err := ioutil.TempFile("", "profatomic") + if err != nil { + t.Fatalf("TempFile: %v", err) + } + defer os.Remove(f.Name()) + defer f.Close() + + if err := StartCPUProfile(f); err != nil { + t.Fatal(err) + } + defer StopCPUProfile() + + var flag uint64 + done := make(chan bool, 1) + + go func() { + for atomic.LoadUint64(&flag) == 0 { + runtime.Gosched() + } + done <- true + }() + time.Sleep(50 * time.Millisecond) + atomic.StoreUint64(&flag, 1) + <-done +} diff --git a/src/runtime/proc.go b/src/runtime/proc.go index a5ada4f6db..ed333bb92e 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -3232,10 +3232,14 @@ var prof struct { hz int32 } -func _System() { _System() } -func _ExternalCode() { _ExternalCode() } -func _LostExternalCode() { _LostExternalCode() } -func _GC() { _GC() } +func _System() { _System() } +func _ExternalCode() { _ExternalCode() } +func _LostExternalCode() { _LostExternalCode() } +func _GC() { _GC() } +func _LostSIGPROFDuringAtomic64() { _LostSIGPROFDuringAtomic64() } + +// Counts SIGPROFs received while in atomic64 critical section, on mips{,le} +var lostAtomic64Count uint64 // Called if we receive a SIGPROF signal. // Called by the signal handler, may run during STW. @@ -3245,6 +3249,21 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { return } + // On mips{,le}, 64bit atomics are emulated with spinlocks, in + // runtime/internal/atomic. If SIGPROF arrives while the program is inside + // the critical section, it creates a deadlock (when writing the sample). + // As a workaround, create a counter of SIGPROFs while in critical section + // to store the count, and pass it to sigprof.add() later when SIGPROF is + // received from somewhere else (with _LostSIGPROFDuringAtomic64 as pc). + if GOARCH == "mips" || GOARCH == "mipsle" { + if f := findfunc(pc); f.valid() { + if hasprefix(funcname(f), "runtime/internal/atomic") { + lostAtomic64Count++ + return + } + } + } + // Profiling runs concurrently with GC, so it must not allocate. // Set a trap in case the code does allocate. // Note that on windows, one thread takes profiles of all the @@ -3371,6 +3390,10 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { } if prof.hz != 0 { + if (GOARCH == "mips" || GOARCH == "mipsle") && lostAtomic64Count > 0 { + cpuprof.addLostAtomic64(lostAtomic64Count) + lostAtomic64Count = 0 + } cpuprof.add(gp, stk[:n]) } getg().m.mallocing-- |