linux-kernel - Re: [PATCH v2 2/2] ext4: protect ext4_release

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Message-ID: <20241126090452.ohggr3daqskllxjk@quack3>
Date: Tue, 26 Nov 2024 10:04:52 +0100
From: Jan Kara <jack@...e.cz>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: linux-ext4@...r.kernel.org, Jan Kara <jack@...e.com>,
	Ritesh Harjani <ritesh.list@...il.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Baokun Li <libaokun1@...wei.com>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v2 2/2] ext4: protect ext4_release_dquot against freezing

On Thu 21-11-24 18:08:55, Ojaswin Mujoo wrote:
> Protect ext4_release_dquot against freezing so that we
> don't try to start a transaction when FS is frozen, leading
> to warnings.
> 
> Further, avoid taking the freeze protection if a transaction
> is already running so that we don't need end up in a deadlock
> as described in
> 
>   46e294efc355 ext4: fix deadlock with fs freezing and EA inodes
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>

Looks good to me (the 0-day reports seem to be due to wrong merge). Feel
free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/super.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 16a4ce704460..f7437a592359 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -6887,12 +6887,25 @@ static int ext4_release_dquot(struct dquot *dquot)
>  {
>  	int ret, err;
>  	handle_t *handle;
> +	bool freeze_protected = false;
> +
> +	/*
> +	 * Trying to sb_start_intwrite() in a running transaction
> +	 * can result in a deadlock. Further, running transactions
> +	 * are already protected from freezing.
> +	 */
> +	if (!ext4_journal_current_handle()) {
> +		sb_start_intwrite(dquot->dq_sb);
> +		freeze_protected = true;
> +	}
>  
>  	handle = ext4_journal_start(dquot_to_inode(dquot), EXT4_HT_QUOTA,
>  				    EXT4_QUOTA_DEL_BLOCKS(dquot->dq_sb));
>  	if (IS_ERR(handle)) {
>  		/* Release dquot anyway to avoid endless cycle in dqput() */
>  		dquot_release(dquot);
> +		if (freeze_protected)
> +			sb_end_intwrite(dquot->dq_sb);
>  		return PTR_ERR(handle);
>  	}
>  	ret = dquot_release(dquot);
> @@ -6903,6 +6916,10 @@ static int ext4_release_dquot(struct dquot *dquot)
>  	err = ext4_journal_stop(handle);
>  	if (!ret)
>  		ret = err;
> +
> +	if (freeze_protected)
> +		sb_end_intwrite(dquot->dq_sb);
> +
>  	return ret;
>  }
>  
> -- 
> 2.43.5
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR