Bug#850182: Please disable TSX in stretch and backport to jessie

[Henrique de Moraes Holschuh <hmh@debian.org>]

On Wed, Jan 4, 2017, at 17:04, Ian Jackson wrote:
> amd64 with TSX is for the purposes of pthreads like a new
> architecture: the locking primitives behave differently and expose
> extra bugs.

Also valid for S/390x, POWER, and anything else where glibc 2.24
supports hardware lock elision.

> These extra bugs will be discovered only by chance (as we see in that
> bug report and in the earlier bugs #843324 and maybe #842796).  As
> more TSX-capable hardware becomes available, we will discover more of
> them, during the life of stretch, when they are hard to fix.
> 
> Also, we don't have the capability to debug them.  I don't think we
> can have a release architecture for stretch that has no porterboxes.

All it takes is an extra "if(unlikely(lock-is-unlocked))
raise(SIGSEGV);" line on the libpthread unlock path for
no-lock-elision).  Or you could generate a warning instead.

That said, I am not speaking against disabling hardware lock elision
acceleration for Debian Stretch.  We might be better off disabling it.

-- 
  Henrique de Moraes Holschuh <hmh@debian.org>