linux-ext4 - Re: [PATCH 0/3 RFC] fs: Hole punch vs page cache filling races

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Date:   Tue, 6 Apr 2021 14:17:02 +0200
From:   Jan Kara <jack@...e.cz>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH 0/3 RFC] fs: Hole punch vs page cache filling races

On Fri 02-04-21 15:34:13, Theodore Ts'o wrote:
> On Wed, Jan 20, 2021 at 05:06:08PM +0100, Jan Kara wrote:
> > 
> > Amir has reported [1] a that ext4 has a potential issues when reads can race
> > with hole punching possibly exposing stale data from freed blocks or even
> > corrupting filesystem when stale mapping data gets used for writeout. The
> > problem is that during hole punching, new page cache pages can get instantiated
> > in a punched range after truncate_inode_pages() has run but before the
> > filesystem removes blocks from the file.  In principle any filesystem
> > implementing hole punching thus needs to implement a mechanism to block
> > instantiating page cache pages during hole punching to avoid this race. This is
> > further complicated by the fact that there are multiple places that can
> > instantiate pages in page cache.  We can have regular read(2) or page fault
> > doing this but fadvise(2) or madvise(2) can also result in reading in page
> > cache pages through force_page_cache_readahead().
> 
> What's the current status of this patch set?  I'm going through
> pending patches and it looks like folks don't like Jan's proposed
> solution.  What are next steps?

Note that I did post v2 here:

https://lore.kernel.org/linux-fsdevel/20210208163918.7871-1-jack@suse.cz/

It didn't get much comments though. I guess I'll rebase the series, include
the explanations I've added in my reply to Dave and resend.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR