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

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Message-ID: <bb732e42-c679-eb26-e87c-b00fd12f65d3@synopsys.com>
Date:   Tue, 10 Nov 2020 19:33:02 +0000
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 11/9/20 2:29 AM, Greg Kroah-Hartman wrote:
> 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@...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.
> Now queued up, thanks.

Thx a bunch Greg.

-Vineet