linux-kernel - Re: [PATCH] Revert "ARC: entry: fix potential EFA clobber when TIF_SYSCALL

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Date:   Sat, 7 Nov 2020 15:10:06 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Waldemar Brodkorb <wbx@...ibc-ng.org>
Subject: Re: [PATCH] Revert "ARC: entry: fix potential EFA clobber when
 TIF_SYSCALL_TRACE"

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@...ibc-ng.org>
> > Bisected-by: Waldemar Brodkorb <wbx@...ibc-ng.org>
> > Cc: stable <stable@...r.kernel.org> # 5.2 and prior
> > Signed-off-by: Vineet Gupta <vgupta@...opsys.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.

thanks,

greg k-h