From: Matthew Wilcox <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org,
Christoph Hellwig <hch@infradead.org>,
Dave Chinner <david@fromorbit.com>,
ceph-devel@vger.kernel.org, Chao Yu <yuchao0@huawei.com>,
Damien Le Moal <damien.lemoal@wdc.com>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Jaegeuk Kim <jaegeuk@kernel.org>,
Jeff Layton <jlayton@kernel.org>,
Johannes Thumshirn <jth@kernel.org>,
linux-cifs@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net, linux-mm@kvack.org,
linux-xfs@vger.kernel.org, Miklos Szeredi <miklos@szeredi.hu>,
Steve French <sfrench@samba.org>, Ted Tso <tytso@mit.edu>
Subject: Re: [PATCH 03/11] mm: Protect operations adding pages to page cache with invalidate_lock
Date: Thu, 13 May 2021 20:38:47 +0100 [thread overview]
Message-ID: <YJ2AR0IURFzz+52G@casper.infradead.org> (raw)
In-Reply-To: <20210513190114.GJ2734@quack2.suse.cz>
On Thu, May 13, 2021 at 09:01:14PM +0200, Jan Kara wrote:
> On Wed 12-05-21 15:40:21, Matthew Wilcox wrote:
> > Remind me (or, rather, add to the documentation) why we have to hold the
> > invalidate_lock during the call to readpage / readahead, and we don't just
> > hold it around the call to add_to_page_cache / add_to_page_cache_locked
> > / add_to_page_cache_lru ? I appreciate that ->readpages is still going
> > to suck, but we're down to just three implementations of ->readpages now
> > (9p, cifs & nfs).
>
> There's a comment in filemap_create_page() trying to explain this. We need
> to protect against cases like: Filesystem with 1k blocksize, file F has
> page at index 0 with uptodate buffer at 0-1k, rest not uptodate. All blocks
> underlying page are allocated. Now let read at offset 1k race with hole
> punch at offset 1k, length 1k.
>
> read() hole punch
> ...
> filemap_read()
> filemap_get_pages()
> - page found in the page cache but !Uptodate
> filemap_update_page()
> locks everything
> truncate_inode_pages_range()
> lock_page(page)
> do_invalidatepage()
> unlock_page(page)
> locks page
> filemap_read_page()
Ah, this is the partial_start case, which means that page->mapping
is still valid. But that means that do_invalidatepage() was called
with (offset 1024, length 1024), immediately after we called
zero_user_segment(). So isn't this a bug in the fs do_invalidatepage()?
The range from 1k-2k _is_ uptodate. It's been zeroed in memory,
and if we were to run after the "free block" below, we'd get that
memory zeroed again.
> ->readpage()
> block underlying offset 1k
> still allocated -> map buffer
> free block under offset 1k
> submit IO -> corrupted data
>
> If you think I should expand it to explain more details, please tell.
> Or maybe I can put more detailed discussion like above into the changelog?
> > Why not:
> >
> > __init_rwsem(&mapping->invalidate_lock, "mapping.invalidate_lock",
> > &sb->s_type->invalidate_lock_key);
>
> I replicated what we do for i_rwsem but you're right, this is better.
> Updated.
Hmm, there's a few places we should use __init_rwsem() ... something
for my "when bored" pile of work.
next prev parent reply other threads:[~2021-05-13 19:39 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 13:46 [PATCH 0/11 v5] fs: Hole punch vs page cache filling races Jan Kara
2021-05-12 13:46 ` [PATCH 01/11] mm: Fix comments mentioning i_mutex Jan Kara
2021-05-12 13:46 ` [PATCH 02/11] documentation: Sync file_operations members with reality Jan Kara
2021-05-12 13:46 ` [PATCH 03/11] mm: Protect operations adding pages to page cache with invalidate_lock Jan Kara
2021-05-12 14:20 ` Matthew Wilcox
2021-05-13 17:49 ` Jan Kara
2021-05-12 14:40 ` Matthew Wilcox
2021-05-13 19:01 ` Jan Kara
2021-05-13 19:38 ` Matthew Wilcox [this message]
2021-05-14 11:07 ` Jan Kara
2021-05-12 15:23 ` Darrick J. Wong
2021-05-13 17:44 ` Jan Kara
2021-05-13 18:52 ` Darrick J. Wong
2021-05-13 23:19 ` Dave Chinner
2021-05-14 16:17 ` Darrick J. Wong
2021-05-17 11:21 ` Jan Kara
2021-05-18 22:36 ` Dave Chinner
2021-05-19 10:57 ` Jan Kara
2021-05-12 13:46 ` [PATCH 04/11] ext4: Convert to use mapping->invalidate_lock Jan Kara
2021-05-12 13:46 ` [PATCH 05/11] ext2: Convert to using invalidate_lock Jan Kara
2021-05-12 13:46 ` [PATCH 06/11] xfs: Convert to use invalidate_lock Jan Kara
2021-05-12 13:46 ` [PATCH 07/11] zonefs: Convert to using invalidate_lock Jan Kara
2021-05-13 0:34 ` Damien Le Moal
2021-05-12 13:46 ` [PATCH 08/11] f2fs: " Jan Kara
2021-05-12 18:00 ` kernel test robot
2021-05-12 13:46 ` [PATCH 09/11] fuse: " Jan Kara
2021-05-12 13:46 ` [PATCH 10/11] ceph: Fix race between hole punch and page fault Jan Kara
2021-05-12 15:19 ` Jeff Layton
2021-05-12 13:46 ` [PATCH 11/11] cifs: " Jan Kara
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