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From: Matthew Wilcox <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>,
	Amir Goldstein <amir73il@gmail.com>,
	Dave Chinner <david@fromorbit.com>, Ted Tso <tytso@mit.edu>,
	ceph-devel@vger.kernel.org, Chao Yu <yuchao0@huawei.com>,
	Damien Le Moal <damien.lemoal@wdc.com>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Hugh Dickins <hughd@google.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>
Subject: Re: [PATCH 02/12] mm: Protect operations adding pages to page cache with invalidate_lock
Date: Fri, 23 Apr 2021 19:30:40 +0100	[thread overview]
Message-ID: <20210423183040.GD235567@casper.infradead.org> (raw)
In-Reply-To: <20210423173018.23133-2-jack@suse.cz>

On Fri, Apr 23, 2021 at 07:29:31PM +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.

One of the things I've had in mind for a while is moving the DAX locked
entry concept into the page cache proper.  It would avoid creating the
new semaphore, at the cost of taking the i_pages lock twice (once to
insert the entries that cover the range, and once to delete the entries).

It'd have pretty much the same effect, though -- read/fault/... would
block until the entry was deleted from the page cache.

  reply	other threads:[~2021-04-23 18:31 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-23 17:29 [PATCH 0/12 v4] fs: Hole punch vs page cache filling races Jan Kara
2021-04-23 17:29 ` [PATCH 02/12] mm: Protect operations adding pages to page cache with invalidate_lock Jan Kara
2021-04-23 18:30   ` Matthew Wilcox [this message]
2021-04-23 23:04   ` Dave Chinner
2021-04-26 15:46     ` Jan Kara
2021-04-23 17:29 ` [PATCH 12/12] cifs: Fix race between hole punch and page fault Jan Kara
2021-04-23 22:07 ` [PATCH 0/12 v4] fs: Hole punch vs page cache filling races Dave Chinner
2021-04-23 23:51   ` Matthew Wilcox
2021-04-24  6:11     ` Christoph Hellwig

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