Re: [PATCH v1] RISC-V: take text_mutex during alternative patching

["Heiko Stübner" <heiko@sntech.de>]

Am Mittwoch, 22. Februar 2023, 18:03:55 CET schrieb Heiko Stübner:
> Am Mittwoch, 22. Februar 2023, 17:47:10 CET schrieb Palmer Dabbelt:
> > On Wed, 22 Feb 2023 07:39:11 PST (-0800), heiko@sntech.de wrote:
> > > Am Mittwoch, 22. Februar 2023, 16:31:25 CET schrieb Andrew Jones:
> > >> On Wed, Feb 22, 2023 at 03:27:43PM +0100, Andrew Jones wrote:
> > >> > On Thu, Feb 16, 2023 at 07:33:55AM -0800, Guenter Roeck wrote:
> > >> > > On 2/15/23 14:00, Heiko Stübner wrote:
> > >> > > [ ... ]
> > >> > > > 
> > >> > > > So now I've also tested Palmer's for-next at
> > >> > > >    commit ec6311919ea6 ("Merge patch series "riscv: Optimize function trace"")
> > >> > > > 
> > >> > > > again with the same variants
> > >> > > > - qemu-riscv32 without zbb
> > >> > > > - qemu-riscv32 with zbb
> > >> > > > - qemu-riscv64 without zbb
> > >> > > > - qemu-riscv64 with zbb
> > >> > > > 
> > >> > > > And all of them booted fine into a nfs-root (debian for riscv64 and a
> > >> > > > buildroot for riscv32).
> > >> > > > 
> > >> > > > I even forced a bug into the zbb code to make sure the patching worked
> > >> > > > correctly (where the kernel failed as expected).
> > >> > > > 
> > >> > > > Qemu-version for me was 7.2.50 (v7.2.0-744-g5a3633929a-dirty)
> > >> > > > 
> > >> > > > I did try the one from Debian-stable (qemu-5.2) but that was too old and
> > >> > > > didn't support Zbb yet.
> > >> > > > 
> > >> > > > One thing of note, the "active" 32bit config I had, somehow didn't produce
> > >> > > > working images and I needed to start a new build using the rv32_defconfig.
> > >> > > > 
> > >> > > > So right now, I'm not sure what more to test though.
> > >> > > > 
> > >> > > 
> > >> > > Another example:
> > >> > > 
> > >> > > - build defconfig
> > >> > > - run
> > >> > >   qemu-system-riscv64 -M virt -m 512M -no-reboot -kernel arch/riscv/boot/Image \
> > >> > >     -snapshot -device virtio-blk-device,drive=d0 -drive file=rootfs.ext2,if=none,id=d0,format=raw \
> > >> > >     -append "root=/dev/vda console=ttyS0,115200 earlycon=uart8250,mmio,0x10000000,115200" \
> > >> > >     -nographic -monitor none
> > >> > > 
> > >> > > With CONFIG_RISCV_ISA_ZBB=y, that results in
> > >> > > 
> > >> > > [    0.818263] /dev/root: Can't open blockdev
> > >> > > [    0.818856] VFS: Cannot open root device "/dev/vda" or unknown-block(0,0): error -6
> > >> > > [    0.819177] Please append a correct "root=" boot option; here are the available partitions:
> > >> > > [    0.819808] fe00           16384 vda
> > >> > > [    0.819944]  driver: virtio_blk
> > >> > > [    0.820534] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
> > >> > > [    0.821101] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.2.0-rc8-next-20230216-00002-g80332825e240 #4
> > >> > > [    0.821672] Hardware name: riscv-virtio,qemu (DT)
> > >> > > [    0.822050] Call Trace:
> > >> > > [    0.822427] [<ffffffff800053e4>] dump_backtrace+0x1c/0x24
> > >> > > [    0.822834] [<ffffffff807f90e4>] show_stack+0x2c/0x38
> > >> > > [    0.823085] [<ffffffff80803aea>] dump_stack_lvl+0x3c/0x54
> > >> > > [    0.823351] [<ffffffff80803b16>] dump_stack+0x14/0x1c
> > >> > > [    0.823601] [<ffffffff807f944c>] panic+0x102/0x29e
> > >> > > [    0.823834] [<ffffffff80a015e2>] mount_block_root+0x18c/0x23e
> > >> > > [    0.824148] [<ffffffff80a0187c>] mount_root+0x1e8/0x218
> > >> > > [    0.824398] [<ffffffff80a019ee>] prepare_namespace+0x142/0x184
> > >> > > [    0.824655] [<ffffffff80a01182>] kernel_init_freeable+0x236/0x25a
> > >> > > [    0.824934] [<ffffffff80804602>] kernel_init+0x1e/0x10a
> > >> > > [    0.825201] [<ffffffff80003560>] ret_from_exception+0x0/0x16
> > >> > > [    0.826180] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) ]---
> > >> > > 
> > >> > > This works fine if CONFIG_RISCV_ISA_ZBB is not enabled.
> > >> > > 
> > >> > > Tested with gcc 11.3, binutils 2.39, qemu v7.2.0 and qemu built from mainline.
> > >> > >
> > >> > 
> > >> > Just to +1 this, I get the same result (unable to mount root fs) with
> > >> > 
> > >> > $QEMU -cpu rv64,zbb=on \
> > >> >         -nographic \
> > >> >         -machine virt \
> > >> >         -kernel $KERNEL \
> > >> >         -append 'root=/dev/vda console=ttyS0' \
> > >> >         -drive file=disk.ext4,format=raw,id=hd0 \
> > >> >         -device virtio-blk-pci,drive=hd0
> > >> > 
> > >> > kernel:   latest riscv-linux/for-next (8658db0a4a0f), defconfig
> > >> > gcc:      riscv-gnu-toolchain (12.1.0)
> > >> > binutils: riscv-gnu-toolchain (2.39)
> > >> > qemu:     latest master (79b677d658d3)
> > >> > 
> > >> > Flipping the QEMU cpu zbb property off allows boot to succeed, i.e. it's
> > >> > not necessary to compile out the CONFIG_RISCV_ISA_ZBB code from the
> > >> > kernel, it's just necessary to avoid using it.
> > >> >
> > >> 
> > >> Looks like something in the strncmp implementation. Only commenting it
> > >> out allows boot to succeed.
> > >
> > > and interestingly it seems to be something very specific. I.e. my setup is
> > > nfsroot-based (qemu is "just" another board in my boardfarm) and booting
> > > into an nfs-root works quite nicely.
> > >
> > > I guess I need to look into how to get an actual disk-image in there.
> > 
> > It looks like Drew isn't using an initrd (and with NFS, presumably you 
> > are)?  That's probably a big difference as well.
> 
> There is no initrd involved in my qemu setup ;-) .
> Just a kernel built from current for-next + defconfig and a nfs-server
> holding a full Debian-riscv64 system.
> 
> 
> The magic qemu incantation is also pretty standard:
> 
> /usr/local/bin/qemu-system-riscv64 -M virt -smp 2 -m 1G -display none \
>  -cpu rv64,zbb=true,zbc=true,svpbmt=true,Zicbom=true,Zawrs=true,sscofpmf=true,v=true \
>  -serial telnet:localhost:5500,server,nowait -kernel /home/devel/nfs/kernel/riscv64/Image \
>  -append earlycon=sbi root=/dev/nfs nfsroot=10.0.2.2:/home/devel/nfs/rootfs-riscv64virt ip=dhcp rw \
>  -netdev user,id=n1 -device virtio-net-pci,netdev=n1 -name boardfarm-0,process=boardfarm-vm-0 -daemonize
> 
> 
> And I also checked that my kernel really lands in the Zbb-code by simply
> adding a "ret" [0] and making sure it breaks vs. runs without it
> 
> 
> Next I'll try to move my rootfs into a real image-file and switch over to
> the commandline Drew calls, to see if it'll reproduce then.

With the rootfs in an image I could reproduce the issue now.

I hacked in a very crude change to find the invocation that acts differently
and voila it's a strncmp of the "/dev/vda" against "/dev/" [0].

It's really strange that all the other invocations produce correct results.




[0]
non-working - with zbb-strncmp:
[    2.619129] strncmp: comparing /dev/vda <-> mtd, count 3 => -1
[    2.620451] strncmp: comparing /dev/vda <-> ubi, count 3 => -1
[    2.621163] strncmp: comparing /dev/vda <-> PARTUUID=, count 9 => -1
[    2.621703] strncmp: comparing /dev/vda <-> PARTLABEL=, count 10 => -1
------ below is the difference
[    2.622255] strncmp: comparing /dev/vda <-> /dev/, count 5 => 1
[    2.623446] strncmp: comparing /dev/vda <-> /dev/, count 5 => 1
------ above is the difference
[    2.627064] strncmp: comparing sysfs <-> ext3, count 4 => 14
[    2.627646] strncmp: comparing tmpfs <-> ext3, count 4 => 15
[    2.628476] strncmp: comparing bdev <-> ext3, count 4 => -3
[    2.628990] strncmp: comparing proc <-> ext3, count 4 => 11
[    2.629422] strncmp: comparing cgroup <-> ext3, count 4 => -2
[    2.629856] strncmp: comparing cgroup2 <-> ext3, count 4 => -2
[    2.630345] strncmp: comparing cpuset <-> ext3, count 4 => -2
[    2.630785] strncmp: comparing devtmpfs <-> ext3, count 4 => -1
[    2.631267] strncmp: comparing debugfs <-> ext3, count 4 => -1
[    2.631696] strncmp: comparing securityfs <-> ext3, count 4 => 1
[    2.632596] strncmp: comparing sockfs <-> ext3, count 4 => 14
[    2.633095] strncmp: comparing bpf <-> ext3, count 4 => -3
[    2.633600] strncmp: comparing pipefs <-> ext3, count 4 => 11
[    2.634071] strncmp: comparing ramfs <-> ext3, count 4 => 13
[    2.634501] strncmp: comparing hugetlbfs <-> ext3, count 4 => 1
[    2.634955] strncmp: comparing rpc_pipefs <-> ext3, count 4 => 1
[    2.635407] strncmp: comparing devpts <-> ext3, count 4 => -1
[    2.638788] strncmp: comparing ext3 <-> ext3, count 4 => 0


working - with normal strncmp:
[    2.416438] strncmp: comparing /dev/vda <-> mtd, count 3 => -62
[    2.417312] strncmp: comparing /dev/vda <-> ubi, count 3 => -70
[    2.418296] strncmp: comparing /dev/vda <-> PARTUUID=, count 9 => -33
[    2.418921] strncmp: comparing /dev/vda <-> PARTLABEL=, count 10 => -33
------ below is the difference
[    2.419450] strncmp: comparing /dev/vda <-> /dev/, count 5 => 0
[    2.420698] strncmp: comparing /dev/vda <-> /dev/, count 5 => 0
------ above is the difference
[    2.424086] strncmp: comparing sysfs <-> ext3, count 4 => 14
[    2.424663] strncmp: comparing tmpfs <-> ext3, count 4 => 15
[    2.425111] strncmp: comparing bdev <-> ext3, count 4 => -3
[    2.425563] strncmp: comparing proc <-> ext3, count 4 => 11
[    2.426022] strncmp: comparing cgroup <-> ext3, count 4 => -2
[    2.426717] strncmp: comparing cgroup2 <-> ext3, count 4 => -2
[    2.427175] strncmp: comparing cpuset <-> ext3, count 4 => -2
[    2.427608] strncmp: comparing devtmpfs <-> ext3, count 4 => -1
[    2.428061] strncmp: comparing debugfs <-> ext3, count 4 => -1
[    2.428526] strncmp: comparing securityfs <-> ext3, count 4 => 14
[    2.428985] strncmp: comparing sockfs <-> ext3, count 4 => 14
[    2.429423] strncmp: comparing bpf <-> ext3, count 4 => -3
[    2.429863] strncmp: comparing pipefs <-> ext3, count 4 => 11
[    2.430433] strncmp: comparing ramfs <-> ext3, count 4 => 13
[    2.431202] strncmp: comparing hugetlbfs <-> ext3, count 4 => 3
[    2.431721] strncmp: comparing rpc_pipefs <-> ext3, count 4 => 13
[    2.432222] strncmp: comparing devpts <-> ext3, count 4 => -1
[    2.432685] strncmp: comparing ext3 <-> ext3, count 4 => 0




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