Re: [PATCH v6 14/14] riscv: Make mmap allocation top-down by default

[Alex Ghiti <alex@ghiti.fr>]

On 10/7/19 8:46 PM, Atish Patra wrote:
> On Mon, 2019-10-07 at 05:11 -0400, Alex Ghiti wrote:
>> On 10/4/19 10:12 PM, Atish Patra wrote:
>>> On Thu, 2019-08-08 at 02:17 -0400, Alexandre Ghiti wrote:
>>>> In order to avoid wasting user address space by using bottom-up
>>>> mmap
>>>> allocation scheme, prefer top-down scheme when possible.
>>>>
>>>> Before:
>>>> root@qemuriscv64:~# cat /proc/self/maps
>>>> 00010000-00016000 r-xp 00000000 fe:00
>>>> 6389       /bin/cat.coreutils
>>>> 00016000-00017000 r--p 00005000 fe:00
>>>> 6389       /bin/cat.coreutils
>>>> 00017000-00018000 rw-p 00006000 fe:00
>>>> 6389       /bin/cat.coreutils
>>>> 00018000-00039000 rw-p 00000000 00:00 0          [heap]
>>>> 1555556000-155556d000 r-xp 00000000 fe:00 7193   /lib/ld-2.28.so
>>>> 155556d000-155556e000 r--p 00016000 fe:00 7193   /lib/ld-2.28.so
>>>> 155556e000-155556f000 rw-p 00017000 fe:00 7193   /lib/ld-2.28.so
>>>> 155556f000-1555570000 rw-p 00000000 00:00 0
>>>> 1555570000-1555572000 r-xp 00000000 00:00 0      [vdso]
>>>> 1555574000-1555576000 rw-p 00000000 00:00 0
>>>> 1555576000-1555674000 r-xp 00000000 fe:00 7187   /lib/libc-
>>>> 2.28.so
>>>> 1555674000-1555678000 r--p 000fd000 fe:00 7187   /lib/libc-
>>>> 2.28.so
>>>> 1555678000-155567a000 rw-p 00101000 fe:00 7187   /lib/libc-
>>>> 2.28.so
>>>> 155567a000-15556a0000 rw-p 00000000 00:00 0
>>>> 3fffb90000-3fffbb1000 rw-p 00000000 00:00 0      [stack]
>>>>
>>>> After:
>>>> root@qemuriscv64:~# cat /proc/self/maps
>>>> 00010000-00016000 r-xp 00000000 fe:00
>>>> 6389       /bin/cat.coreutils
>>>> 00016000-00017000 r--p 00005000 fe:00
>>>> 6389       /bin/cat.coreutils
>>>> 00017000-00018000 rw-p 00006000 fe:00
>>>> 6389       /bin/cat.coreutils
>>>> 2de81000-2dea2000 rw-p 00000000 00:00 0          [heap]
>>>> 3ff7eb6000-3ff7ed8000 rw-p 00000000 00:00 0
>>>> 3ff7ed8000-3ff7fd6000 r-xp 00000000 fe:00 7187   /lib/libc-
>>>> 2.28.so
>>>> 3ff7fd6000-3ff7fda000 r--p 000fd000 fe:00 7187   /lib/libc-
>>>> 2.28.so
>>>> 3ff7fda000-3ff7fdc000 rw-p 00101000 fe:00 7187   /lib/libc-
>>>> 2.28.so
>>>> 3ff7fdc000-3ff7fe2000 rw-p 00000000 00:00 0
>>>> 3ff7fe4000-3ff7fe6000 r-xp 00000000 00:00 0      [vdso]
>>>> 3ff7fe6000-3ff7ffd000 r-xp 00000000 fe:00 7193   /lib/ld-2.28.so
>>>> 3ff7ffd000-3ff7ffe000 r--p 00016000 fe:00 7193   /lib/ld-2.28.so
>>>> 3ff7ffe000-3ff7fff000 rw-p 00017000 fe:00 7193   /lib/ld-2.28.so
>>>> 3ff7fff000-3ff8000000 rw-p 00000000 00:00 0
>>>> 3fff888000-3fff8a9000 rw-p 00000000 00:00 0      [stack]
>>>>
>>>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>>>> Acked-by: Paul Walmsley <paul.walmsley@sifive.com>
>>>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>>>> Reviewed-by: Kees Cook <keescook@chromium.org>
>>>> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
>>>> ---
>>>>    arch/riscv/Kconfig | 12 ++++++++++++
>>>>    1 file changed, 12 insertions(+)
>>>>
>>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>>> index 59a4727ecd6c..87dc5370becb 100644
>>>> --- a/arch/riscv/Kconfig
>>>> +++ b/arch/riscv/Kconfig
>>>> @@ -54,6 +54,18 @@ config RISCV
>>>>    	select EDAC_SUPPORT
>>>>    	select ARCH_HAS_GIGANTIC_PAGE
>>>>    	select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
>>>> +	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
>>>> +	select HAVE_ARCH_MMAP_RND_BITS
>>>> +
>>>> +config ARCH_MMAP_RND_BITS_MIN
>>>> +	default 18 if 6legacy_va_layout4BIT
>>>> +	default 8
>>>> +
>>>> +# max bits determined by the following formula:
>>>> +#  VA_BITS - PAGE_SHIFT - 3
>>>> +config ARCH_MMAP_RND_BITS_MAX
>>>> +	default 24 if 64BIT # SV39 based
>>>> +	default 17
>>>>    
>>>>    config MMU
>>>>    	def_bool y
>>> With this patch, I am not able to boot a Fedora Linux(a Gnome
>>> desktop
>>> image) on RISC-V hardware (Unleashed + Microsemi Expansion board).
>>> The
>>> booting gets stuck right after systemd starts.
>>>
>>> https://paste.fedoraproject.org/paste/TOrUMqqKH-pGFX7CnfajDg
>>>
>>> Reverting just this patch allow to boot Fedora successfully on
>>> specific
>>> RISC-V hardware. I have not root caused the issue but it looks like
>>> it
>>> might have messed userpsace mapping.
>> It might have messed userspace mapping but not enough to make
>> userspace
>> completely broken
>> as systemd does some things. I would try to boot in legacy layout:
>> if
>> you can try to set sysctl legacy_va_layout
>> at boottime, it will map userspace as it was before (bottom-up). If
>> that
>> does not work, the problem could
>> be the randomization that is activated by default now.
> Randomization may not be the issue. I just removed
> ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT from the config and that seems to
> work. Here is the bottom-up layout with randomization on.

Oups, sorry for my previous answer, I missed yours that landed in 
another folder.

Removing ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT also removes randomization
as this config selects ARCH_HAS_ELF_RANDOMIZE.
You could remove ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and selects by hand
ARCH_HAS_ELF_RANDOMIZE but you would have to implement arch_mmap_rnd and
arch_randomize_brk (elf-randomize.h).

The simplest would be to boot in legacy layout: I did not find a way to 
set this in kernel
command line, but you can by modifying it directly in the code:

https://elixir.bootlin.com/linux/v5.4-rc2/source/kernel/sysctl.c#L269

> [root@fedora-riscv ~]# cat /proc/self/maps
> 1555556000-1555570000 r-xp 00000000 103:01
> 280098                        /usr/lib64/ld-2.28.so
> 1555570000-1555571000 r--p 00019000 103:01
> 280098                        /usr/lib64/ld-2.28.so
> 1555571000-1555572000 rw-p 0001a000 103:01
> 280098                        /usr/lib64/ld-2.28.so
> 1555572000-1555573000 rw-p 00000000 00:00 0
> 1555573000-1555575000 r-xp 00000000 00:00
> 0                              [vdso]
> 1555575000-1555576000 r--p 00000000 103:01
> 50936                         /usr/lib/locale/en_US.utf8/LC_IDENTIFICAT
> ION
> 1555576000-155557d000 r--s 00000000 103:01
> 280826                        /usr/lib64/gconv/gconv-modules.cache
> 155557d000-155557e000 r--p 00000000 103:01
> 50937                         /usr/lib/locale/en_US.utf8/LC_MEASUREMENT
> 155557e000-155557f000 r--p 00000000 103:01
> 50939                         /usr/lib/locale/en_US.utf8/LC_TELEPHONE
> 155557f000-1555580000 r--p 00000000 103:01
> 3706                          /usr/lib/locale/en_US.utf8/LC_ADDRESS
> 1555580000-1555581000 r--p 00000000 103:01
> 50944                         /usr/lib/locale/en_US.utf8/LC_NAME
> 1555581000-1555582000 r--p 00000000 103:01
> 3775                          /usr/lib/locale/en_US.utf8/LC_PAPER
> 1555582000-1555583000 r--p 00000000 103:01
> 3758                          /usr/lib/locale/en_US.utf8/LC_MESSAGES/SY
> S_LC_MESSAGES
> 1555583000-1555584000 r--p 00000000 103:01
> 50938                         /usr/lib/locale/en_US.utf8/LC_MONETARY
> 1555584000-1555585000 r--p 00000000 103:01
> 50940                         /usr/lib/locale/en_US.utf8/LC_TIME
> 1555585000-1555586000 r--p 00000000 103:01
> 50945                         /usr/lib/locale/en_US.utf8/LC_NUMERIC
> 1555590000-1555592000 rw-p 00000000 00:00 0
> 1555592000-15556b1000 r-xp 00000000 103:01
> 280105                        /usr/lib64/libc-2.28.so
> 15556b1000-15556b5000 r--p 0011e000 103:01
> 280105                        /usr/lib64/libc-2.28.so
> 15556b5000-15556b7000 rw-p 00122000 103:01
> 280105                        /usr/lib64/libc-2.28.so
> 15556b7000-15556bb000 rw-p 00000000 00:00 0
> 15556bb000-1555933000 r--p 00000000 103:01
> 3755                          /usr/lib/locale/en_US.utf8/LC_COLLATE
> 1555933000-1555986000 r--p 00000000 103:01
> 50942                         /usr/lib/locale/en_US.utf8/LC_CTYPE
> 1555986000-15559a8000 rw-p 00000000 00:00 0
> 2aaaaaa000-2aaaab1000 r-xp 00000000 103:01
> 283975                        /usr/bin/cat
> 2aaaab1000-2aaaab2000 r--p 00006000 103:01
> 283975                        /usr/bin/cat
> 2aaaab2000-2aaaab3000 rw-p 00007000 103:01
> 283975                        /usr/bin/cat
> 2aaaab3000-2aaaad4000 rw-p 00000000 00:00
> 0                              [heap]
> 3fffc97000-3fffcb8000 rw-p 00000000 00:00
> 0                              [stack]
>
>
>> Anyway, it's weird since userspace should not depend on how the
>> mapping is.
>>
>> If you can identify the program that stalls, that would be fantastic
>> :)
>>
> It stucks while booting. So I am not sure how to figure out which
> program stalls. It is difficult to figure out from boot log as it
> stucks at different places but soon after systemd starts.

If you can attach the running kernel, I would use vmlinux-gdb.py commands
to figure out which processes are running (lx-ps command in particular could
give us a hint). You can also add traces directly in the kernel and 
either use
lx-dmesg command to print them from gdb or use your standard serial output:
I would then print task_struct->comm at context switch to see which process
is stuck.
To use the python script, you need to recompile with DEBUG_INFO and
GDB_SCRIPTS enabled.

FYI, I have just booted a custom buildroot image based on kernel 5.4-rc2.

Let me know if I can do anything.

Alex

>> As the code is common to mips and arm now and I did not hear from
>> them,
>> I imagine the problem comes
>> from us.
>>
>> Alex