linux-kernel - Re: [PATCH] arch: um: kernel: skas: mmu: remove pmd_free() and pud_free() for failure processing in init_stub

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Date:	Wed, 13 Nov 2013 17:14:13 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Richard Weinberger <richard@....at>
CC:	Jeff Dike <jdike@...toit.com>, Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	uml-user <user-mode-linux-user@...ts.sourceforge.net>
Subject: Re: [PATCH] arch: um: kernel: skas: mmu: remove pmd_free() and pud_free()
 for failure processing in init_stub_pte()

On 11/13/2013 05:07 PM, Richard Weinberger wrote:
> Am 13.11.2013 06:06, schrieb Chen Gang:
>> Unfortunately, p?d_alloc() and p?d_free() are not pair!! If p?d_alloc()
>> succeed, they may be used, so in the next failure, we have to skip them
>> to let exit_mmap() or do_munmap() to process it.
>>
>> According to "Documentation/vm/locking", 'mm->page_table_lock' is for
>> using vma list, so not need it when its related vmas are detached or
>> unmapped from using vma list.
>>
>> The related work flow:
>>
>>   exit_mmap() ->
>>     unmap_vmas(); /* so not need mm->page_table_lock */
>>     free_pgtables();
>>
>>   do_munmap()->
>>     detach_vmas_to_be_unmapped(); /* so not need mm->page_table_lock */
>>     unmap_region() ->
>>       free_pgtables();
>>
>>   free_pgtables() ->
>>     free_pgd_range() ->
>>       free_pud_range() ->
>>         free_pmd_range() ->
>>           free_pte_range() ->
>>             pmd_clear();
>>             pte_free_tlb();
>>           pud_clear();
>>           pmd_free_tlb();
>>         pgd_clear(); 
>>         pud_free_tlb();
>>
>>
>> Signed-off-by: Chen Gang <gang.chen@...anux.com>
> 
> Sounds reasonable to me.
> *But* there are patches you from out there that tried to fix similar issues and got reverted later.
> Now I'm a bit nervous and want a ACK from mm folks to have this verified.
> It's not that I don't trust you, but I really don't trust you. ;-)
> 

OK, thanks.

> Thanks,
> //richard
> 
> 

-- 
Chen Gang
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