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

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Message-ID: <Z0XB6uLUkwDWLV8E@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com>
Date: Tue, 26 Nov 2024 18:11:14 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: Jan Kara <jack@...e.cz>
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>
Subject: Re: [PATCH v2 2/2] ext4: protect ext4_release_dquot against freezing

On Tue, Nov 26, 2024 at 10:04:52AM +0100, Jan Kara wrote:
> 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

Thanks Jan, yes it does seem like an incorrect merge.

> 
> > ---
> >  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