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

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Message-ID: <Y91QNz+U/MGs9cPc@slm.duckdns.org>
Date:   Fri, 3 Feb 2023 08:19:35 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-ext4@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>, stable@...r.kernel.org
Subject: Re: [PATCH] ext4: fix cgroup writeback accounting with fs-layer
 encryption

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.

-- 
tejun