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

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Date:   Fri, 2 Apr 2021 15:34:13 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     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 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?

Thanks,

					- Ted