[PATCH v4 15/19] lib/crc32: make crc32c() go directly to lib

[Askar Safin]

Eric Biggers <ebiggers at kernel.org>:
> Now that the lower level __crc32c_le() library function is optimized for

This patch (i. e. 38a9a5121c3b ("lib/crc32: make crc32c() go directly to lib"))
solves actual bug I found in practice. So, please, backport it
to stable kernels.

I did bisect.

It is possible to apply this patch on top of v6.12.48 without conflicts.

The bug actually prevents me for using my system (more details below).

Here is steps to reproduce bug I noticed.

Build kernel so:

$ cat /tmp/mini
CONFIG_64BIT=y
CONFIG_PRINTK=y
CONFIG_SERIAL_8250=y
CONFIG_TTY=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_BLK_DEV_INITRD=y
CONFIG_RD_GZIP=y
CONFIG_BINFMT_ELF=y
CONFIG_BINFMT_SCRIPT=y
CONFIG_PROC_FS=y
CONFIG_SYSFS=y
CONFIG_DEVTMPFS=y
CONFIG_MODULES=y
CONFIG_BTRFS_FS=m
CONFIG_MODULE_COMPRESS=y
CONFIG_MODULE_COMPRESS_XZ=y
CONFIG_MODULE_COMPRESS_ALL=y
CONFIG_MODULE_DECOMPRESS=y
CONFIG_PRINTK_TIME=y
$ make allnoconfig KCONFIG_ALLCONFIG=/tmp/mini
$ make

Then create initramfs, which contains statically built busybox
(I used busybox v1.37.0 (Debian 1:1.37.0-6+b3)) and modules we just created.

Then run Qemu using command line similar to this:

qemu-system-x86_64 -kernel arch/x86/boot/bzImage -initrd i.gz -append 'console=ttyS0 panic=1 rdinit=/bin/busybox sh' -m 256 -no-reboot -enable-kvm -serial stdio -display none

Then in busybox shell type this:

# mkdir /proc
# busybox mount -t proc proc /proc
# modprobe btrfs

On buggy kernels I get this output:

# modprobe btrfs
[   19.614228] raid6: skipped pq benchmark and selected sse2x4
[   19.614638] raid6: using intx1 recovery algorithm
[   19.616569] xor: measuring software checksum speed
[   19.616937]    prefetch64-sse  : 42616 MB/sec
[   19.617270]    generic_sse     : 41320 MB/sec
[   19.617531] xor: using function: prefetch64-sse (42616 MB/sec)
[   19.619731] Invalid ELF header magic: != ELF
modprobe: can't load module libcrc32c (kernel/lib/libcrc32c.ko.xz): unknown symbol in module, or unknown parameter

The bug is reproducible on all kernels from v6.12 until this commit.
And it is not reproducible on all kernels, which contain this commit.
I found this using bisect.

This bug actually breaks my workflow. I have btrfs as root filesystem.
Initramfs, generated by Debian, doesn't suit my needs. So I'm going
to create my own initramfs from scratch. (Note that I use Debian Trixie,
which has v6.12.48 kernel.) During testing this initramfs in Qemu
I noticed that command "modprobe btrfs" fails with error given above.
(I not yet tried to test this initramfs on real hardware.)

So, this bug actually breaks my workflow.

So, please backport this patch (i. e. 38a9a5121c3b ("lib/crc32: make crc32c() go directly to lib"))
to stable kernels.

I tested that this patch can be applied without conflicts on top of v6.12.48,
and this patch indeed fixes the bug for v6.12.48.

If you want, I can give more info.

It is possible that this is in fact bug in busybox, not in Linux.
But still I think that backporting this patch is good idea.

This busybox thread my be related:
https://lists.busybox.net/pipermail/busybox/2023-May/090309.html

-- 
Askar Safin