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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id a4sm8527275oif.3.2020.09.16.19.05.09 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Wed, 16 Sep 2020 19:05:11 -0700 (PDT) Date: Wed, 16 Sep 2020 19:04:46 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Dave Chinner cc: Jan Kara , Amir Goldstein , Andreas Gruenbacher , Theodore Tso , Martin Brandenburg , Mike Marshall , Damien Le Moal , Jaegeuk Kim , Qiuyang Sun , linux-xfs , linux-fsdevel , Linux MM , linux-kernel , Matthew Wilcox , Linus Torvalds , "Kirill A. Shutemov" , Andrew Morton , Al Viro , nborisov@suse.de Subject: Re: More filesystem need this fix (xfs: use MMAPLOCK around filemap_map_pages()) In-Reply-To: <20200917014454.GZ12131@dread.disaster.area> Message-ID: References: <20200623052059.1893966-1-david@fromorbit.com> <20200916155851.GA1572@quack2.suse.cz> <20200917014454.GZ12131@dread.disaster.area> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 17 Sep 2020, Dave Chinner wrote: > > So.... > > P0 p1 > > hole punch starts > takes XFS_MMAPLOCK_EXCL > truncate_pagecache_range() > unmap_mapping_range(start, end) > > > do_fault_around() > ->map_pages > filemap_map_pages() > page mapping valid, > page is up to date > maps PTEs > > truncate_inode_pages_range() > truncate_cleanup_page(page) > invalidates page > delete_from_page_cache_batch(page) > frees page > No. filemap_map_pages() checks page->mapping after trylock_page(), before setting up the pte; and truncate_cleanup_page() does a one-page unmap_mapping_range() if page_mapped(), while holding page lock. (Of course, there's a different thread, in which less reliance on page lock is being discussed, but that would be a future thing.) Hugh