Re: Bisected stability regression in 6.6

[Bagas Sanjaya]

On Sat, Nov 11, 2023 at 01:31:01AM -0500, 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@xxxxxx>
> 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@xxxxxx>
> 
>  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(-)
> 
> I have tried applying ad4aa06e1d92b06ed56c7240252927bd60632efe ("parisc: Add
> nop instructions after TLB inserts") on top of 6.6, but it does NOT fix the
> issue.
> 
> Let me know if there is anything I can answer on this.  I can provide full
> remote access with BMC if it would help.

Thanks for the regression report. I'm adding it to regzbot:

#regzbot ^introduced: 3033cd4307681c

-- 
An old man doll... just what I always wanted! - Clara

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