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

From: Atish Patra
Date: Tue Oct 08 2019 - 22:07:56 EST

On Tue, 2019-10-08 at 07:58 -0400, Alex Ghiti wrote:
> 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@xxxxxxxx>
> > > > > Acked-by: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
> > > > > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> > > > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > > > Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> > > > > ---
> > > > > 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).
>

Ahh okay.

> 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
>

Setting this to 1 works.

> > [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_IDENTIF
> > ICAT
> > 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_MEASURE
> > MENT
> > 155557e000-155557f000 r--p 00000000 103:01
> > 50939 /usr/lib/locale/en_US.utf8/LC_TELEPHO
> > NE
> > 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_MESSAGE
> > S/SY
> > S_LC_MESSAGES
> > 1555583000-1555584000 r--p 00000000 103:01
> > 50938 /usr/lib/locale/en_US.utf8/LC_MONETAR
> > Y
> > 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.
>

vmlinux-gdb.py works only if you are running in Qemu or have a JTAG.
Right ?

I am seeing this issue only on HiFive Unleashed + Microsemi Expansion
board with Fedora Gnome desktop image. I can even boot a Fedora
developer image on same hardware and a busybox image in Unleashed
without any issues. But the issue is not specific to fedora as we see
the same issue in OpenEmbedded disk image as well (HiFive Unleashed +
Microsemi Expansion board).

May be it gets triggerd only if bigger userspace ?


> 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

--
Regards,
Atish