Re: [akpm-mm:mm-unstable] [mm] 85ad413389: BUG:kernel_NULL_pointer_dereference,address

[Oliver Sang]

hi, Suren Baghdasaryan,

On Sun, Dec 08, 2024 at 06:09:05PM -0800, Suren Baghdasaryan wrote:
> On Sun, Dec 8, 2024 at 7:26 AM kernel test robot <oliver.sang@xxxxxxxxx> wrote:
> >
> >
> >
> > Hello,
> >
> > kernel test robot noticed "BUG:kernel_NULL_pointer_dereference,address" on:
> >
> > commit: 85ad413389aec04cfaaba043caa8128b76c6e491 ("mm: make vma cache SLAB_TYPESAFE_BY_RCU")
> > https://git.kernel.org/cgit/linux/kernel/git/akpm/mm.git mm-unstable
> >
> > in testcase: boot
> >
> > config: i386-randconfig-141-20241208
> > compiler: gcc-11
> > test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> >
> > (please refer to attached dmesg/kmsg for entire log/backtrace)
> >
> >
> > +------------------------------------------------+------------+------------+
> > |                                                | 98d5eefb97 | 85ad413389 |
> > +------------------------------------------------+------------+------------+
> > | BUG:kernel_NULL_pointer_dereference,address    | 0          | 12         |
> > | Oops                                           | 0          | 12         |
> > | EIP:lock_anon_vma_root                         | 0          | 12         |
> > | Kernel_panic-not_syncing:Fatal_exception       | 0          | 12         |
> > +------------------------------------------------+------------+------------+
> >
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > | Closes: https://lore.kernel.org/oe-lkp/202412082208.db1fb2c9-lkp@xxxxxxxxx
> 
> Thanks for the report!
> It looks like anon_vma passed to lock_anon_vma_root() is NULL but it's
> not obvious to me why my patch would cause that.
> 
> Oliver, how can I reproduce this locally?
> 

To reproduce:

        # build kernel
	cd linux
	cp config-6.13.0-rc1-00162-g85ad413389ae .config
	make -j$(nproc) HOSTCC=gcc-11 CC=gcc-11 ARCH=i386 olddefconfig prepare modules_prepare bzImage modules
	make -j$(nproc) HOSTCC=gcc-11 CC=gcc-11 ARCH=i386 INSTALL_MOD_PATH=<mod-install-dir> modules_install
	cd <mod-install-dir>
	find lib/ | cpio -o -H newc --quiet | gzip > modules.cgz


        git clone https://github.com/intel/lkp-tests.git
        cd lkp-tests
        bin/lkp qemu -k <bzImage> -m modules.cgz job-script # job-script is attached in this email

        # if come across any failure that blocks the test,
        # please remove ~/.lkp and /lkp dir to run from a clean state.


config and job-script files are attached in original report.

one thing we want to mention is this seems only reproducible with i386 config in
our tests.