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Date: Tue, 15 Oct 2019 00:31:37 +0000
From: Atish Patra <Atish.Patra@....com>
To: "alex@...ti.fr" <alex@...ti.fr>
CC: "ralf@...ux-mips.org" <ralf@...ux-mips.org>,
"keescook@...omium.org" <keescook@...omium.org>,
"palmer@...ive.com" <palmer@...ive.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
"catalin.marinas@....com" <catalin.marinas@....com>,
"paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux@...linux.org.uk" <linux@...linux.org.uk>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"paul.burton@...s.com" <paul.burton@...s.com>,
"will.deacon@....com" <will.deacon@....com>,
"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
"hch@....de" <hch@....de>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"jhogan@...nel.org" <jhogan@...nel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
"mcgrof@...nel.org" <mcgrof@...nel.org>
Subject: Re: [PATCH v6 14/14] riscv: Make mmap allocation top-down by default
On Wed, 2019-10-09 at 14:39 -0400, Alex Ghiti wrote:
> On 10/8/19 10:07 PM, Atish Patra wrote:
> > 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@...uriscv64:~# 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@...uriscv64:~# 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@...ti.fr>
> > > > > > > Acked-by: Paul Walmsley <paul.walmsley@...ive.com>
> > > > > > > Reviewed-by: Christoph Hellwig <hch@....de>
> > > > > > > Reviewed-by: Kees Cook <keescook@...omium.org>
> > > > > > > Reviewed-by: Luis Chamberlain <mcgrof@...nel.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).
> > >
> > 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@...ora-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_IDE
> > > > NTIF
> > > > 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_MEA
> > > > SURE
> > > > MENT
> > > > 155557e000-155557f000 r--p 00000000 103:01
> > > > 50939 /usr/lib/locale/en_US.utf8/LC_TEL
> > > > EPHO
> > > > NE
> > > > 155557f000-1555580000 r--p 00000000 103:01
> > > > 3706 /usr/lib/locale/en_US.utf8/LC_ADD
> > > > RESS
> > > > 1555580000-1555581000 r--p 00000000 103:01
> > > > 50944 /usr/lib/locale/en_US.utf8/LC_NAM
> > > > E
> > > > 1555581000-1555582000 r--p 00000000 103:01
> > > > 3775 /usr/lib/locale/en_US.utf8/LC_PAP
> > > > ER
> > > > 1555582000-1555583000 r--p 00000000 103:01
> > > > 3758 /usr/lib/locale/en_US.utf8/LC_MES
> > > > SAGE
> > > > S/SY
> > > > S_LC_MESSAGES
> > > > 1555583000-1555584000 r--p 00000000 103:01
> > > > 50938 /usr/lib/locale/en_US.utf8/LC_MON
> > > > ETAR
> > > > Y
> > > > 1555584000-1555585000 r--p 00000000 103:01
> > > > 50940 /usr/lib/locale/en_US.utf8/LC_TIM
> > > > E
> > > > 1555585000-1555586000 r--p 00000000 103:01
> > > > 50945 /usr/lib/locale/en_US.utf8/LC_NUM
> > > > ERIC
> > > > 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_COL
> > > > LATE
> > > > 1555933000-1555986000 r--p 00000000 103:01
> > > > 50942 /usr/lib/locale/en_US.utf8/LC_CTY
> > > > PE
> > > > 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 ?
>
> Yes. Does the problem appear on qemu too ?
>
Nope.
> > 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 ?
>
> The purpose of this patch is, on the contrary, to not lose address
> space by
> setting an arbitrary starting point (TASK_UNMAPPED_BASE) for mmap.
>
> Do you a link to an image that fails to boot and reproduce the
> problem
> on Qemu ?
>
Nope. This is only reproducible in RISC-V Fedora Gnome desktop image on
a HiFive Unleashed + Microsemi Expansion. Just to clarify, there is no
issue with OpenEmbedded disk image related to memory layout. It was a
userspace thing.
Unforunately, fedora builders do not build gnome images now and the one
I am using is very old (~ 1 year). I think I can just use the sysctl
parameter for now in my tree and live with it until we have Fedora 31
images availale. We can revisit the problem after that. Thanks for
suggestions.
> I don't have much idea here, the only thing I can think of is
> finding
> the application
> that makes the boot stall and understand what is wrong.
>
> > > 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
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