linux-kernel - Re: [PATCH] ubifs: Get/put page when changing PG

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Date:   Tue, 25 Dec 2018 10:42:37 +0800
From:   zhangjun <openzhangj@...il.com>
To:     Richard Weinberger <richard@....at>, linux-mtd@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hsiangkao@...l.ru, kirill.shutemov@...ux.intel.com,
        stable@...r.kernel.org
Subject: Re: [PATCH] ubifs: Get/put page when changing PG_private

On 2018/12/21 下午4:56, Richard Weinberger wrote:
> Am Samstag, 15. Dezember 2018, 16:01:30 CET schrieb Richard Weinberger:
>> The page migration code assumes that a page with PG_private
>> set has its page count elevated by 1.
>> UBIFS never did this and therefore the migration code was unable
>> to migrate some pages owned by UBIFS.
>> The lead to situations where the CMA memory allocator failed to
>> allocate memory.
>>
>> Fix this by using get/put_page when changing PG_private.
>>
>> Cc: <stable@...r.kernel.org>
>> Cc: zhangjun <openzhangj@...il.com>
>> Fixes: 4ac1c17b2044 ("UBIFS: Implement ->migratepage()")
>> Reported-by: zhangjun <openzhangj@...il.com>
>> Signed-off-by: Richard Weinberger <richard@....at>
> FYI, on the XFS side a similar change caused a regression.
> https://marc.info/?l=linux-fsdevel&m=154530861202448&w=2
>
> Until this regression is not fully understood, including the implications
> for UBIFS, I'll not merge this patch.
>
> Thanks,
> //richard
>
>
Hello,richard


Before fully understanding this regression, in order to fix the bug of 
cma_alloc(),
submit a conservative patch that modifies count in iomap_migrate_page().
Can you consider merging first?

https://marc.info/?l=linux-kernel&m=154473132332661&w=2


Thanks
//zhangjun