From: Jan Kara <jack@suse.cz>
To: Matthew Wilcox <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>,
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 21:01:14 +0200 [thread overview]
Message-ID: <20210513190114.GJ2734@quack2.suse.cz> (raw)
In-Reply-To: <YJvo1bGG1tG+gtgC@casper.infradead.org>
On Wed 12-05-21 15:40:21, Matthew Wilcox wrote:
> On Wed, May 12, 2021 at 03:46:11PM +0200, Jan Kara wrote:
> > Currently, serializing operations such as page fault, read, or readahead
> > against hole punching is rather difficult. The basic race scheme is
> > like:
> >
> > fallocate(FALLOC_FL_PUNCH_HOLE) read / fault / ..
> > truncate_inode_pages_range()
> > <create pages in page
> > cache here>
> > <update fs block mapping and free blocks>
> >
> > Now the problem is in this way read / page fault / readahead can
> > instantiate pages in page cache with potentially stale data (if blocks
> > get quickly reused). Avoiding this race is not simple - page locks do
> > not work because we want to make sure there are *no* pages in given
> > range. inode->i_rwsem does not work because page fault happens under
> > mmap_sem which ranks below inode->i_rwsem. Also using it for reads makes
> > the performance for mixed read-write workloads suffer.
> >
> > So create a new rw_semaphore in the address_space - invalidate_lock -
> > that protects adding of pages to page cache for page faults / reads /
> > readahead.
>
> 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()
->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?
> Also, could I trouble you to run the comments through 'fmt' (or
> equivalent)? It's easier to read if you're not kissing right up on 80
> columns.
Sure, will do.
> > +++ b/fs/inode.c
> > @@ -190,6 +190,9 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
> > mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
> > mapping->private_data = NULL;
> > mapping->writeback_index = 0;
> > + init_rwsem(&mapping->invalidate_lock);
> > + lockdep_set_class(&mapping->invalidate_lock,
> > + &sb->s_type->invalidate_lock_key);
>
> 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.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2021-05-13 19:01 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 [this message]
2021-05-13 19:38 ` Matthew Wilcox
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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