runtime: simplify sigprof traceback interlocking
runtime: simplify sigprof traceback interlocking

The addition of stack barrier locking to copystack subsumes the
partial fix from commit bbd1a1c for SIGPROF during copystack. With the
stack barrier locking, this commit simplifies the rule in sigprof to:
the user stack can be traced only if sigprof can acquire the stack
barrier lock.

Updates #12932, #13362.

Change-Id: I1c1f80015053d0ac7761e9e0c7437c2aba26663f
Reviewed-on: https://go-review.googlesource.com/17192
Run-TryBot: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

binarycrusader/go,Endika/go,deft-code/go,momchil-velikov/go,binarycrusader/go,roth1002/go,akutz/go,mwhudson/go,miolini/go,goodlang/good,vanloswang/go,cloudflare/go,vanloswang/go,vanloswang/go,Endika/go,josharian/go,cloudflare/go,mwhudson/go,roth1002/go,vsekhar/elastic-go,linux-on-ibm-z/go,nawawi/go,theif519/go,polyverse-security/go,mwhudson/go,Samurais/go,CAFxX/go,Cofyc/go,ganboing/go-esx,ImJasonH/go,deft-code/go,4ad/go,miolini/go,roth1002/go,4ad/go,codestation/go,josharian/go,momchil-velikov/go,linux-on-ibm-z/go,deft-code/go,Cofyc/go,sndnvaps/go,mwhudson/go,Cofyc/go,momchil-velikov/go,josharian/go,codestation/go,goodlang/good,CAFxX/go,theif519/go,binarycrusader/go,ImJasonH/go,derekmarcotte/go,CAFxX/go,sndnvaps/go,vanloswang/go,deft-code/go,linux-on-ibm-z/go,Samurais/go,sndnvaps/go,vsekhar/elastic-go,akutz/go,polyverse-security/go,roth1002/go,4ad/go,Cofyc/go,Endika/go,vsekhar/elastic-go,cyberroadie/go,linux-on-ibm-z/go,josharian/go,CAFxX/go,linux-on-ibm-z/go,deft-code/go,CAFxX/go,kim-racktop/go,CAFxX/go,sndnvaps/go,kim-racktop/go,nawawi/go,josharian/go,suncycheng/go,suncycheng/go,golang/go,linux-on-ibm-z/go,mwhudson/go,momchil-velikov/go,akutz/go,polyverse-security/go,roth1002/go,polyverse-security/go,nawawi/go,derekmarcotte/go,mwhudson/go,vsekhar/elastic-go,ganboing/go-esx,suncycheng/go,binarycrusader/go,codestation/go,Endika/go,suncycheng/go,miolini/go,miolini/go,binarycrusader/go,goodlang/good,sndnvaps/go,nawawi/go,goodlang/good,ImJasonH/go,theif519/go,codestation/go,momchil-velikov/go,Cofyc/go,momchil-velikov/go,cloudflare/go,mwhudson/go,4ad/go,linux-on-ibm-z/go,cloudflare/go,deft-code/go,binarycrusader/go,cyberroadie/go,golang/go,momchil-velikov/go,kim-racktop/go,kim-racktop/go,kim-racktop/go,polyverse-security/go,golang/go,golang/go,CAFxX/go,CAFxX/go,Endika/go,josharian/go,nawawi/go,theif519/go,cloudflare/go,sndnvaps/go,ganboing/go-esx,polyverse-security/go,polyverse-security/go,kim-racktop/go,Cofyc/go,roth1002/go,codestation/go,christopher-henderson/Go,cyberroadie/go,ImJasonH/go,binarycrusader/go,suncycheng/go,ganboing/go-esx,ImJasonH/go,josharian/go,nawawi/go,vsekhar/elastic-go,nawawi/go,goodlang/good,ganboing/go-esx,sndnvaps/go,kim-racktop/go,derekmarcotte/go,ImJasonH/go,kim-racktop/go,vsekhar/elastic-go,Endika/go,cyberroadie/go,sndnvaps/go,polyverse-security/go,akutz/go,vanloswang/go,cloudflare/go,goodlang/good,cyberroadie/go,theif519/go,deft-code/go,Endika/go,suncycheng/go,ganboing/go-esx,4ad/go,theif519/go,codestation/go,goodlang/good,codestation/go,codestation/go,nawawi/go,vanloswang/go,Samurais/go,Samurais/go,josharian/go,ganboing/go-esx,mwhudson/go,linux-on-ibm-z/go,4ad/go,suncycheng/go,4ad/go,goodlang/good,derekmarcotte/go,miolini/go,Endika/go,derekmarcotte/go,ImJasonH/go,vsekhar/elastic-go,Samurais/go,derekmarcotte/go,ImJasonH/go,Cofyc/go,golang/go,suncycheng/go,akutz/go,cloudflare/go,golang/go,vsekhar/elastic-go,miolini/go,cloudflare/go,binarycrusader/go,Samurais/go,miolini/go,vanloswang/go,miolini/go,Samurais/go,cyberroadie/go,vanloswang/go,deft-code/go,theif519/go,Samurais/go,akutz/go,golang/go,derekmarcotte/go,cyberroadie/go,Cofyc/go,roth1002/go,derekmarcotte/go,akutz/go,theif519/go,cyberroadie/go,momchil-velikov/go,ganboing/go-esx,golang/go,4ad/go,roth1002/go,akutz/go