linux-ext4 - Re: [PATCH] ext4: fix cgroup writeback accounting with fs-layer encryption

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Date:   Tue, 7 Mar 2023 11:52:20 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        Tejun Heo <tj@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH] ext4: fix cgroup writeback accounting with fs-layer
 encryption

On Fri, Feb 03, 2023 at 08:19:35AM -1000, Tejun Heo wrote:
> On Thu, Feb 02, 2023 at 04:55:03PM -0800, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@...gle.com>
> > 
> > When writing a page from an encrypted file that is using
> > filesystem-layer encryption (not inline encryption), ext4 encrypts the
> > pagecache page into a bounce page, then writes the bounce page.
> > 
> > It also passes the bounce page to wbc_account_cgroup_owner().  That's
> > incorrect, because the bounce page is a newly allocated temporary page
> > that doesn't have the memory cgroup of the original pagecache page.
> > This makes wbc_account_cgroup_owner() not account the I/O to the owner
> > of the pagecache page as it should.
> > 
> > Fix this by always passing the pagecache page to
> > wbc_account_cgroup_owner().
> > 
> > Fixes: 001e4a8775f6 ("ext4: implement cgroup writeback support")
> > Cc: stable@...r.kernel.org
> > Reported-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> 
> Acked-by: Tejun Heo <tj@...nel.org>
> 
> Thanks.

This patch hasn't been applied yet.  Ted, I was hoping you would take it through
the ext4 tree.  Can you do so when you have a chance?

- Eric