Re: [mm] 763ecb0350: kernel_BUG_at_mm/mmap.c

[Yu Zhao]

On Wed, Oct 5, 2022 at 9:30 AM kernel test robot <oliver.sang@xxxxxxxxx> wrote:
>
>
> Greeting,
>
> FYI, we noticed the following commit (built with gcc-11):
>
> commit: 763ecb035029f500d7e6dc99acd1ad299b7726a1 ("mm: remove the vma linked list")
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>
> in testcase: trinity
> version: trinity-static-i386-x86_64-1c734c75-1_2020-01-06
> with following parameters:
>
>         runtime: 300s
>         group: group-03
>
> test-description: Trinity is a linux system call fuzz tester.
> test-url: http://codemonkey.org.uk/projects/trinity/
>
>
> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
>
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>
>
>
> If you fix the issue, kindly add following tag
> | Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> | Link: https://lore.kernel.org/r/202210052318.5ad10912-oliver.sang@xxxxxxxxx
>
>
> [   63.390267][ T5018] ------------[ cut here ]------------
> [   63.391875][ T5018] kernel BUG at mm/mmap.c:3167!
> [   63.393264][ T5018] invalid opcode: 0000 [#1] SMP PTI
> [   63.394501][ T5018] CPU: 1 PID: 5018 Comm: trinity-c1 Not tainted 6.0.0-rc3-00284-g763ecb035029 #1
> [   63.396050][ T5018] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
> [ 63.397726][ T5018] RIP: 0010:exit_mmap (mm/mmap.c:3167 (discriminator 1))

Thanks, Oliver.

The attached dmesg doesn't say much. My guess is the oom reaper jumped
in between

        mmap_read_unlock(mm);

        /*
         * Set MMF_OOM_SKIP to hide this task from the oom killer/reaper
         * because the memory has been already freed.
         */
        set_bit(MMF_OOM_SKIP, &mm->flags);
        mmap_write_lock(mm);

It seems to me we need to hold the lock for write all the time. But
there is probably a reason we didn't do it in the first place.