linux-ext4 - Re: [PATCH 08/15] fsverity: kick off hash readahead at data I/O submission time

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Message-ID: <20260130055541.GC622@lst.de>
Date: Fri, 30 Jan 2026 06:55:41 +0100
From: Christoph Hellwig <hch@....de>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Eric Biggers <ebiggers@...nel.org>, Christoph Hellwig <hch@....de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	David Sterba <dsterba@...e.com>, Theodore Ts'o <tytso@....edu>,
	Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
	Andrey Albershteyn <aalbersh@...hat.com>,
	Matthew Wilcox <willy@...radead.org>, linux-fsdevel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net, fsverity@...ts.linux.dev
Subject: Re: [PATCH 08/15] fsverity: kick off hash readahead at data I/O
 submission time

On Wed, Jan 28, 2026 at 03:22:13PM -0800, Darrick J. Wong wrote:
> > Unfortunately, this patch causes recursive down_read() of
> > address_space::invalidate_lock.  How was this meant to work?
> 
> Usually the filesystem calls filemap_invalidate_lock{,_shared} if it
> needs to coordinate truncate vs. page removal (i.e. fallocate hole
> punch).  That said, there are a few places where the pagecache itself
> will take that lock too...

> [...]

> ...except that pagecache_ra_unbounded is being called recursively from
> an actual file data read.  My guess is that we'd need a flag or
> something to ask for "unlocked" readahead if we still want readahead to
> spur more readahead.

Basically just move it out of page_cache_ra_unbounded.  With the
consolidation in the earlier patches there are just two callers
of page_cache_ra_unbounded left, this and the redirty_blocks() in f2fs.

I'd kinda wish to kill the latter, as the past-EOF reading is something
that should be restricted to core code, but I can't really think of
an easy way to do that.