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Date: Sat, 11 Nov 2023 18:33:42 -0500
From: matoro <matoro_mailinglist_kernel@...oro.tk>
To: Sam James <sam@...too.org>
Cc: Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Bisected stability regression in 6.6
On 2023-11-11 16:27, Sam James wrote:
> Helge Deller <deller@....de> writes:
>
>> On 11/11/23 07:31, matoro wrote:
>>> Hi Helge, I have bisected a regression in 6.6 which is causing
>>> userspace segfaults at a significantly increased rate in kernel 6.6.
>>> There seems to be a pathological case triggered by the ninja build
>>> tool. The test case I have been using is cmake with ninja backend to
>>> attempt to build the nghttp2 package. In 6.6, this segfaults, not at
>>> the same location every time, but with enough reliability that I was
>>> able to use it as a bisection regression case, including immediately
>>> after a reboot. In the kernel log, these show up as "trap #15: Data
>>> TLB miss fault" messages. Now these messages can and do show up in
>>> 6.5 causing segfaults, but never immediately after a reboot and
>>> infrequently enough that the system is stable. With kernel 6.6 I am
>>> completely unable to build nghttp2 under any circumstances.
>>>
>>> I have bisected this down to the following commit:
>>>
>>> $ git bisect good
>>> 3033cd4307681c60db6d08f398a64484b36e0b0f is the first bad commit
>>> commit 3033cd4307681c60db6d08f398a64484b36e0b0f
>>> Author: Helge Deller <deller@....de>
>>> Date: Sat Aug 19 00:53:28 2023 +0200
>>>
>>> parisc: Use generic mmap top-down layout and brk randomization
>>>
>>> parisc uses a top-down layout by default that exactly fits the
>>> generic
>>> functions, so get rid of arch specific code and use the generic
>>> version
>>> by selecting ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT.
>>>
>>> Note that on parisc the stack always grows up and a "unlimited stack"
>>> simply means that the value as defined in
>>> CONFIG_STACK_MAX_DEFAULT_SIZE_MB
>>> should be used. So RLIM_INFINITY is not an indicator to use the
>>> legacy
>>> memory layout.
>>>
>>> Signed-off-by: Helge Deller <deller@....de>
>>>
>>> arch/parisc/Kconfig | 17 +++++++++++++
>>> arch/parisc/kernel/process.c | 14 -----------
>>> arch/parisc/kernel/sys_parisc.c | 54
>>> +----------------------------------------
>>> mm/util.c | 5 +++-
>>> 4 files changed, 22 insertions(+), 68 deletions(-)
>>
>> Thanks for your report!
>> I think it's quite unlikely that this patch introduces such a bad
>> regression.
>> I'd suspect some other bad commmit, but I'll try to reproduce.
>
> matoro, does a revert apply cleanly? Does it help?
Yes, I just tested this and it cleanly reverts on linux-6.6.y and the revert
does fix the issue.
>>
>> In any case, do you have CONFIG_BPF_JIT enabled? If so, could you try
>> to reproduce with CONFIG_BPF_JIT disabled?
>> The JIT is quite new in v6.6 and I did face some crashes and disabling
>> it helped me so far.
>>
>>> I have tried applying ad4aa06e1d92b06ed56c7240252927bd60632efe
>>> ("parisc: Add nop instructions after TLB inserts") on top of 6.6, but
>>> it does NOT fix the issue.
>>
>> Ok.
>>
>> Helge
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