From afae876b3189711c49f9d2cb197081f41c9f3979 Mon Sep 17 00:00:00 2001 From: philhofer Date: Wed, 6 Jun 2018 12:05:36 -0700 Subject: [PATCH] runtime: fix pprof livelock on arm On 32-bit architectures without native 64-bit atomic instructions, 64-bit atomics are emulated using spinlocks. However, the sigprof handling code expects to be able to perform 64-bit atomic operations in signal handlers. Spinning on an acquired spinlock in a signal handler leads to a livelock. This is issue #20146. The original fix for #20146 did not include arm in the list of architectures that need to work around portability issues in the sigprof handler code. The unit test designed to catch this issue does not fail on arm builds because arm uses striped spinlocks, and thus the livelock takes many minutes to reproduce. This is issue #24260. (This patch doesn't completely fix #24260 on go1.10.2 due to issue #25785, which is probably related to the arm cas kernel helpers. Those have been removed at tip.) With this patch applied, I was able to run the reproducer for issue #24260 for more than 90 minutes without reproducing the livelock. Without this patch, the livelock took as little as 8 minutes to reproduce. Fixes #20146 Updates #24260 Change-Id: I64bf53a14d53c4932367d919ac55e17c99d87484 Reviewed-on: https://go-review.googlesource.com/117057 Run-TryBot: Philip Hofer TryBot-Result: Gobot Gobot Reviewed-by: Brad Fitzpatrick Reviewed-by: Cherry Zhang --- src/runtime/proc.go | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/runtime/proc.go b/src/runtime/proc.go index 1267899b83..e3549d367a 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -3699,7 +3699,7 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { // 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 GOARCH == "mips" || GOARCH == "mipsle" || GOARCH == "arm" { if f := findfunc(pc); f.valid() { if hasprefix(funcname(f), "runtime/internal/atomic") { lostAtomic64Count++ @@ -3839,7 +3839,7 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { } if prof.hz != 0 { - if (GOARCH == "mips" || GOARCH == "mipsle") && lostAtomic64Count > 0 { + if (GOARCH == "mips" || GOARCH == "mipsle" || GOARCH == "arm") && lostAtomic64Count > 0 { cpuprof.addLostAtomic64(lostAtomic64Count) lostAtomic64Count = 0 } -- 2.50.0