Re: mm: mmap_sem lock assertion failure in __mlock_vma_pages_range

[Davidlohr Bueso]

On Tue, 2014-03-11 at 15:39 -0400, Sasha Levin wrote:
> Hi all,
> 
> I've ended up deleting the log file by mistake, but this bug does seem to be 
> important
> so I'd rather not wait before the same issue is triggered again.
> 
> The call chain is:
> 
>       mlock (mm/mlock.c:745)
>               __mm_populate (mm/mlock.c:700)
>                       __mlock_vma_pages_range (mm/mlock.c:229)
>                               VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));

So __mm_populate() is only called by mlock(2) and this VM_BUG_ON seems
wrong as we call it without the lock held:

        up_write(&current->mm->mmap_sem);
        if (!error)
                error = __mm_populate(start, len, 0);
        return error;
}

> 
> It seems to be a rather simple trace triggered from userspace. The only 
> recent patch
> in the area (that I've noticed) was "mm/mlock: prepare params outside 
> critical region".
> I've reverted it and trying to testing without it.

Odd, this patch should definitely *not* cause this. In any case every
operation removed from the critical region is local to the function:

        lock_limit = rlimit(RLIMIT_MEMLOCK);
        lock_limit >>= PAGE_SHIFT;
        locked = len >> PAGE_SHIFT;

        down_write(&current->mm->mmap_sem);

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/