Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 12 Jul 2018 16:42:10 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To:     Hugh Dickins <hughd@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Ashwin Chaugule <ashwinch@google.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] thp: fix data loss when splitting a file pmd
Message-ID: <20180712134210.d7kzlubl6runpfkr@black.fi.intel.com>
References: <alpine.LSU.2.11.1807111741430.1106@eggly.anvils>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <alpine.LSU.2.11.1807111741430.1106@eggly.anvils>
User-Agent: NeoMutt/20170714-126-deb55f (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Jul 12, 2018 at 12:48:54AM +0000, Hugh Dickins wrote:
> __split_huge_pmd_locked() must check if the cleared huge pmd was dirty,
> and propagate that to PageDirty: otherwise, data may be lost when a huge
> tmpfs page is modified then split then reclaimed.
> 
> How has this taken so long to be noticed?  Because there was no problem
> when the huge page is written by a write system call (shmem_write_end()
> calls set_page_dirty()), nor when the page is allocated for a write fault
> (fault_dirty_shared_page() calls set_page_dirty()); but when allocated
> for a read fault (which MAP_POPULATE simulates), no set_page_dirty().

Yeah... Sorry.

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov