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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