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runtime: drop SIGPROF while in ARM < 7 kernel helpers

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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 <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>
This commit is contained in:
Michael Pratt 2021-08-12 17:17:51 -04:00
parent 4c8ffb3baa
commit 20a620fd9f
1 changed files with 8 additions and 1 deletions
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9
src/runtime/proc.go
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@ -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.