From 20a620fd9f7bc35739c1af3602d53808d0430814 Mon Sep 17 00:00:00 2001 From: Michael Pratt Date: Thu, 12 Aug 2021 17:17:51 -0400 Subject: [PATCH] runtime: drop SIGPROF while in ARM < 7 kernel helpers On Linux ARMv6 and below runtime/internal/atomic.Cas calls into a kernel cas helper at a fixed address. If a SIGPROF arrives while executing the kernel helper, the sigprof lostAtomic logic will miss that we are potentially in the spinlock critical section, which could cause a deadlock when using atomics later in sigprof. Fixes #47505 Change-Id: If8ba0d0fc47e45d4e6c68eca98fac4c6ed4e43c1 Reviewed-on: https://go-review.googlesource.com/c/go/+/341889 Trust: Michael Pratt Run-TryBot: Michael Pratt Reviewed-by: Michael Knyszek Reviewed-by: Cherry Mui TryBot-Result: Go Bot --- src/runtime/proc.go | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/src/runtime/proc.go b/src/runtime/proc.go index ec4be31db3..764f12769e 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -4619,7 +4619,7 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { return } - // On mips{,le}, 64bit atomics are emulated with spinlocks, in + // On mips{,le}/arm, 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 @@ -4632,6 +4632,13 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { return } } + if GOARCH == "arm" && goarm < 7 && GOOS == "linux" && pc&0xffff0000 == 0xffff0000 { + // runtime/internal/atomic functions call into kernel + // helpers on arm < 7. See + // runtime/internal/atomic/sys_linux_arm.s. + cpuprof.lostAtomic++ + return + } } // Profiling runs concurrently with GC, so it must not allocate.