From mboxrd@z Thu Jan  1 00:00:00 1970
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From: Richard Weinberger <richard@nod.at>
To: linux-mtd@lists.infradead.org
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        hsiangkao@mail.ru, kirill.shutemov@linux.intel.com,
        stable@vger.kernel.org, zhangjun <openzhangj@gmail.com>
Subject: Re: [PATCH] ubifs: Get/put page when changing PG_private
Date: Fri, 21 Dec 2018 09:56:25 +0100
Message-ID: <386368225.TvJUPtmGVW@blindfold>
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References: <20181215150130.19381-1-richard@nod.at>
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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@vger.kernel.org>
> Cc: zhangjun <openzhangj@gmail.com>
> Fixes: 4ac1c17b2044 ("UBIFS: Implement ->migratepage()")
> Reported-by: zhangjun <openzhangj@gmail.com>
> Signed-off-by: Richard Weinberger <richard@nod.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