From: Michael Pratt <mpratt@google.com>
Date: Thu, 12 Aug 2021 21:17:51 +0000 (-0400)
Subject: [release-branch.go1.17] runtime: drop SIGPROF while in ARM < 7 kernel helpers
X-Git-Tag: go1.17~2
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=f7b9470992bfae96fe61d45bec40b7fc282f15f0;p=gostls13.git

[release-branch.go1.17] 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.

For #47505
Fixes #47688

Change-Id: If8ba0d0fc47e45d4e6c68eca98fac4c6ed4e43c1
Reviewed-on: https://go-review.googlesource.com/c/go/+/341889
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
(cherry picked from commit 20a620fd9f7bc35739c1af3602d53808d0430814)
Reviewed-on: https://go-review.googlesource.com/c/go/+/341890
---

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 7bc2a92590..a144b36ec8 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -4686,7 +4686,7 @@ 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
@@ -4699,6 +4699,13 @@ 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.