linux-kernel - Re: swap file broken with ext4 fast-commit

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Message-ID: <20201024133846.GA33750@xps-13-7390>
Date:   Sat, 24 Oct 2020 15:38:46 +0200
From:   Andrea Righi <andrea.righi@...onical.com>
To:     Harshad Shirwadkar <harshadshirwadkar@...il.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: swap file broken with ext4 fast-commit

On Sat, Oct 24, 2020 at 03:13:37PM +0200, Andrea Righi wrote:
> I'm getting the following error if I try to create and activate a swap
> file defined on an ext4 filesystem:
> 
>  [   34.406479] swapon: file is not committed
> 
> The swap file is created in the root filesystem (ext4 mounted with the
> following options):
> 
> $ grep " / " /proc/mounts
> /dev/vda1 / ext4 rw,relatime 0 0
> 
> No matter how long I wait or how many times I run sync, I'm still
> getting the same error and the swap file is never activated.
> 
> A git bisect shows that this issue has been introduced by the following
> commit:
> 
>  aa75f4d3daae ("ext4: main fast-commit commit path")
> 
> Simple test case to reproduce the problem:
> 
>  # fallocate -l 8G /swapfile
>  # chmod 0600 /swapfile
>  # mkswap /swapfile
>  # swapon /swapfile
> 
> Maybe we're missing to mark the inode as clean somewhere, even if the
> transation is committed to the journal?

I think I see the problem. There's something wrong in
ext4_inode_datasync_dirty(), it looks like the logic to check if the
inode is dirty is quite the opposite.

I'll test and send a patch soon.

-Andrea