Re: [PATCH v2 2/2] ext4: protect ext4_release_dquot against freezing

Ojaswin Mujoo
2024-11-26T12:41:31Z

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@suse.cz>
> > Signed-off-by: Ojaswin Mujoo <ojaswin@linux.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@suse.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@suse.com>
> SUSE Labs, CR