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SubjectRe: [LKP] dd2283f260 [ 97.263072] WARNING:at_kernel/locking/lockdep.c:#lock_downgrade
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On 11/20/18 4:57 PM, Kirill A. Shutemov wrote:
> On Fri, Nov 16, 2018 at 08:56:04AM -0800, Yang Shi wrote:
>>> a8dda165ec vfree: add debug might_sleep()
>>> dd2283f260 mm: mmap: zap pages with read mmap_sem in munmap
>>> 5929a1f0ff Merge tag 'riscv-for-linus-4.20-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/riscv-linux
>>> 0bc80e3cb0 Add linux-next specific files for 20181114
>>> +-----------------------------------------------------+------------+------------+------------+---------------+
>>> | | a8dda165ec | dd2283f260 | 5929a1f0ff | next-20181114 |
>>> +-----------------------------------------------------+------------+------------+------------+---------------+
>>> | boot_successes | 314 | 178 | 190 | 168 |
>>> | boot_failures | 393 | 27 | 21 | 40 |
>>> | WARNING:held_lock_freed | 383 | 23 | 17 | 39 |
>>> | is_freeing_memory#-#,with_a_lock_still_held_there | 383 | 23 | 17 | 39 |
>>> | BUG:unable_to_handle_kernel | 5 | 2 | 4 | 1 |
>>> | Oops:#[##] | 9 | 3 | 4 | 1 |
>>> | EIP:debug_check_no_locks_freed | 9 | 3 | 4 | 1 |
>>> | Kernel_panic-not_syncing:Fatal_exception | 9 | 3 | 4 | 1 |
>>> | Mem-Info | 4 | 1 | | |
>>> | invoked_oom-killer:gfp_mask=0x | 1 | 1 | | |
>>> | WARNING:at_kernel/locking/lockdep.c:#lock_downgrade | 0 | 6 | 4 | 7 |
>>> | EIP:lock_downgrade | 0 | 6 | 4 | 7 |
>>> +-----------------------------------------------------+------------+------------+------------+---------------+
>>>
>>> [ 96.288009] random: get_random_u32 called from arch_rnd+0x3c/0x70 with crng_init=0
>>> [ 96.359626] input_id (331) used greatest stack depth: 6360 bytes left
>>> [ 96.749228] grep (358) used greatest stack depth: 6336 bytes left
>>> [ 96.921470] network.sh (341) used greatest stack depth: 6212 bytes left
>>> [ 97.262340]
>>> [ 97.262587] =========================
>>> [ 97.263072] WARNING: held lock freed!
>>> [ 97.263536] 4.19.0-06969-gdd2283f #1 Not tainted
>>> [ 97.264110] -------------------------
>>> [ 97.264575] udevd/198 is freeing memory 9c16c930-9c16c99b, with a lock still held there!
>>> [ 97.265542] (ptrval) (&anon_vma->rwsem){....}, at: unlink_anon_vmas+0x14e/0x420
>>> [ 97.266450] 1 lock held by udevd/198:
>>> [ 97.266924] #0: (ptrval) (&mm->mmap_sem){....}, at: __do_munmap+0x531/0x730
>> I have not figured out what this is caused by. But, the below warning looks
>> more confusing. This might be caused by the below one.
> I *think* we need to understand more about what detached VMAs mean for
> rmap. The anon_vma for these VMAs still reachable for the rmap and
> therefore VMA too. I don't quite grasp what is implications of this, but
> it doesn't look good.

I'm supposed before accessing anon_vma, VMA need to be found by
find_vma() first, right? But, finding VMA need hold mmap_sem, once
detach VMAs is called, others should not be able to find the VMAs
anymore. So, the anon_vma should not be reachable except the munmap caller.

>
> I'll look into this more when I get some free cycles.

I'm still traveling, will definitely look into it further once I'm back.

Thanks,
Yang

>
> It's better to disable the optimization for now (by ignoring 'downgrade'
> in __do_munmap()). Before it hits release.
>

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