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Subject: Re: [mm] b1f0502d04: INFO:trying_to_register_non-static_key
To:     David Rientjes <rientjes@google.com>
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From:   Laurent Dufour <ldufour@linux.vnet.ibm.com>
Date:   Thu, 5 Apr 2018 18:55:35 +0200
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On 04/04/2018 23:53, David Rientjes wrote:
> On Wed, 4 Apr 2018, Laurent Dufour wrote:
> 
>>> I also think the following is needed:
>>>
>>> diff --git a/fs/exec.c b/fs/exec.c
>>> --- a/fs/exec.c
>>> +++ b/fs/exec.c
>>> @@ -312,6 +312,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
>>>  	vma->vm_flags = VM_SOFTDIRTY | VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
>>>  	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>>>  	INIT_LIST_HEAD(&vma->anon_vma_chain);
>>> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
>>> +	seqcount_init(&vma->vm_sequence);
>>> +	atomic_set(&vma->vm_ref_count, 0);
>>> +#endif
>>>
>>>  	err = insert_vm_struct(mm, vma);
>>>  	if (err)
>>
>> No, this not needed because the vma is allocated with kmem_cache_zalloc() so
>> vm_ref_count is 0, and insert_vm_struc() will later call
>> __vma_link_rb() which will call seqcount_init().
>>
>> Furhtermore, in case of error, the vma structure is freed without calling
>> get_vma() so there is risk of lockdep warning.
>>
> 
> Perhaps you're working from a different tree than I am, or you fixed the 
> lockdep warning differently when adding to dup_mmap() and mmap_region().
> 
> I got the following two lockdep errors.
> 
> I fixed it locally by doing the seqcount_init() and atomic_set() 
> everywhere a vma could be initialized.

That's weird, I don't get that on my side with lockdep activated.

There is a call to seqcount_init() in dup_mmap(), in mmap_region() and
__vma_link_rb() and that's enough to cover all the case.

That's being said, it'll be better call seqcount_init each time as soon as a
vma structure is allocated. For the vm_ref_count value, as most of the time the
vma is zero allocated, I don't think this is needed.
I just have to check when new_vma = *old_vma is done, but this often just
follow a vma allocation.
> 
> INFO: trying to register non-static key.
> the code is fine but needs lockdep annotation.
> turning off the locking correctness validator.
> CPU: 12 PID: 1 Comm: init Not tainted
> Call Trace:
>  [<ffffffff8b12026f>] dump_stack+0x67/0x98
>  [<ffffffff8a92b616>] register_lock_class+0x1e6/0x4e0
>  [<ffffffff8a92cfe9>] __lock_acquire+0xb9/0x1710
>  [<ffffffff8a92ef3a>] lock_acquire+0xba/0x200
>  [<ffffffff8aa827df>] mprotect_fixup+0x10f/0x310
>  [<ffffffff8aade3fd>] setup_arg_pages+0x12d/0x230
>  [<ffffffff8ab4564a>] load_elf_binary+0x44a/0x1740
>  [<ffffffff8aadde9b>] search_binary_handler+0x9b/0x1e0
>  [<ffffffff8ab44e96>] load_script+0x206/0x270
>  [<ffffffff8aadde9b>] search_binary_handler+0x9b/0x1e0
>  [<ffffffff8aae0355>] do_execveat_common.isra.32+0x6b5/0x9d0
>  [<ffffffff8aae069c>] do_execve+0x2c/0x30
>  [<ffffffff8a80047b>] run_init_process+0x2b/0x30
>  [<ffffffff8b1358d4>] kernel_init+0x54/0x110
>  [<ffffffff8b2001ca>] ret_from_fork+0x3a/0x50
> 
> and
> 
> INFO: trying to register non-static key.
> the code is fine but needs lockdep annotation.
> turning off the locking correctness validator.
> CPU: 21 PID: 1926 Comm: mkdir Not tainted
> Call Trace:
>  [<ffffffff985202af>] dump_stack+0x67/0x98
>  [<ffffffff97d2b616>] register_lock_class+0x1e6/0x4e0
>  [<ffffffff97d2cfe9>] __lock_acquire+0xb9/0x1710
>  [<ffffffff97d2ef3a>] lock_acquire+0xba/0x200
>  [<ffffffff97e73c09>] unmap_page_range+0x89/0xaa0
>  [<ffffffff97e746af>] unmap_single_vma+0x8f/0x100
>  [<ffffffff97e74a1b>] unmap_vmas+0x4b/0x90
>  [<ffffffff97e7f833>] exit_mmap+0xa3/0x1c0
>  [<ffffffff97cc1b23>] mmput+0x73/0x120
>  [<ffffffff97ccbacd>] do_exit+0x2bd/0xd60
>  [<ffffffff97ccc5b7>] SyS_exit+0x17/0x20
>  [<ffffffff97c01f1d>] do_syscall_64+0x6d/0x1a0
>  [<ffffffff9860005a>] entry_SYSCALL_64_after_hwframe+0x26/0x9b
> 
> I think it would just be better to generalize vma allocation to initialize 
> certain fields and init both spf fields properly for 
> CONFIG_SPECULATIVE_PAGE_FAULT.  It's obviously too delicate as is.
>