[PATCH] Revert "ARC: entry: fix potential EFA clobber when TIF_SYSCALL_TRACE"

[Greg Kroah-Hartman]

On Sat, Nov 07, 2020 at 03:10:06PM +0100, Greg Kroah-Hartman wrote:
> On Fri, Nov 06, 2020 at 08:27:44PM +0000, Vineet Gupta wrote:
> > Hi Stable Team,
> > 
> > On 10/19/20 7:19 PM, Vineet Gupta wrote:
> > > This reverts commit 00fdec98d9881bf5173af09aebd353ab3b9ac729.
> > > (but only from 5.2 and prior kernels)
> > > 
> > > The original commit was a preventive fix based on code-review and was
> > > auto-picked for stable back-port (for better or worse).
> > > It was OK for v5.3+ kernels, but turned up needing an implicit change
> > > 68e5c6f073bcf70 "(ARC: entry: EV_Trap expects r10 (vs. r9) to have
> > >  exception cause)" merged in v5.3 which itself was not backported.
> > > So to summarize the stable backport of this patch for v5.2 and prior
> > > kernels is busted and it won't boot.
> > > 
> > > The obvious solution is backport 68e5c6f073bcf70 but that is a pain as
> > > it doesn't revert cleanly and each of affected kernels (so far v4.19,
> > > v4.14, v4.9, v4.4) needs a slightly different massaged varaint.
> > > So the easier fix is to simply revert the backport from 5.2 and prior.
> > > The issue was not a big deal as it would cause strace to sporadically
> > > not work correctly.
> > > 
> > > Waldemar Brodkorb first reported this when running ARC uClibc regressions
> > > on latest stable kernels (with offending backport). Once he bisected it,
> > > the analysis was trivial, so thx to him for this.
> > > 
> > > Reported-by: Waldemar Brodkorb <wbx at uclibc-ng.org>
> > > Bisected-by: Waldemar Brodkorb <wbx at uclibc-ng.org>
> > > Cc: stable <stable at vger.kernel.org> # 5.2 and prior
> > > Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
> > 
> > Can this revert be please applied to 4.19 and older kernels for the next cycle.
> > 
> > Or is there is a procedural issue given this revert is not in mainline. I've
> > described the issue in detail above so if there's a better/desirable way of
> > reverting it from backports, please let me know.
> 
> THis is fine, sorry, it's just in a backlog of lots of stable patches...
> 
> We will get to it soon.

Now queued up, thanks.

gre gk-h