Re: [PATCH v2] ocfs2: fix circular locking dependency in ocfs2_acquire_dquot

[syzbot <syzbot+51244a05705883616c95@syzkaller.appspotmail.com>]

> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

This crash does not have a reproducer. I cannot test it.

> master
>
> diff --git a/fs/ocfs2/quota_global.c b/fs/ocfs2/quota_global.c
> index e85b1ccf81be..95bb901820cf 100644
> --- a/fs/ocfs2/quota_global.c
> +++ b/fs/ocfs2/quota_global.c
> @@ -821,13 +821,35 @@ static int ocfs2_acquire_dquot(struct dquot *dquot)
>         trace_ocfs2_acquire_dquot(from_kqid(&init_user_ns, dquot->dq_id),
>                                   type);
>         mutex_lock(&dquot->dq_lock);
> +
> +       /*
> +        * Speculatively extend quota file before acquiring any locks or
> +        * starting transaction to avoid lock inversion. sb_start_intwrite
> +        * (via ocfs2_start_trans) ranks above quota file locks.
> +        */
> +       if (need_alloc) {
> +               WARN_ON(journal_current_handle());
> +               status = ocfs2_extend_no_holes(gqinode, NULL,
> +                       i_size_read(gqinode) + (need_alloc <<
> sb->s_blocksize_bits),
> +                       i_size_read(gqinode));
> +               if (status < 0)
> +                       goto out;
> +       }
> +
> +       handle = ocfs2_start_trans(osb,
> +                                  ocfs2_calc_global_qinit_credits(sb, type));
> +       if (IS_ERR(handle)) {
> +               status = PTR_ERR(handle);
> +               goto out;
> +       }
> +
>         /*
>          * We need an exclusive lock, because we're going to update use count
>          * and instantiate possibly new dquot structure
>          */
>         status = ocfs2_lock_global_qf(info, 1);
>         if (status < 0)
> -               goto out;
> +               goto out_trans;
>         status = ocfs2_qinfo_lock(info, 0);
>         if (status < 0)
>                 goto out_dq;
> @@ -843,29 +865,12 @@ static int ocfs2_acquire_dquot(struct dquot *dquot)
>         OCFS2_DQUOT(dquot)->dq_use_count++;
>         OCFS2_DQUOT(dquot)->dq_origspace = dquot->dq_dqb.dqb_curspace;
>         OCFS2_DQUOT(dquot)->dq_originodes = dquot->dq_dqb.dqb_curinodes;
> -       if (!dquot->dq_off) {   /* No real quota entry? */
> +       if (!dquot->dq_off)     /* No real quota entry? */
>                 ex = 1;
> -               /*
> -                * Add blocks to quota file before we start a transaction since
> -                * locking allocators ranks above a transaction start
> -                */
> -               WARN_ON(journal_current_handle());
> -               status = ocfs2_extend_no_holes(gqinode, NULL,
> -                       i_size_read(gqinode) + (need_alloc <<
> sb->s_blocksize_bits),
> -                       i_size_read(gqinode));
> -               if (status < 0)
> -                       goto out_dq;
> -       }
>
> -       handle = ocfs2_start_trans(osb,
> -                                  ocfs2_calc_global_qinit_credits(sb, type));
> -       if (IS_ERR(handle)) {
> -               status = PTR_ERR(handle);
> -               goto out_dq;
> -       }
>         status = ocfs2_qinfo_lock(info, ex);
>         if (status < 0)
> -               goto out_trans;
> +               goto out_dq;
>         status = qtree_write_dquot(&info->dqi_gi, dquot);
>         if (ex && info_dirty(sb_dqinfo(sb, type))) {
>                 err = __ocfs2_global_write_info(sb, type);
> @@ -873,10 +878,10 @@ static int ocfs2_acquire_dquot(struct dquot *dquot)
>                         status = err;
>         }
>         ocfs2_qinfo_unlock(info, ex);
> -out_trans:
> -       ocfs2_commit_trans(osb, handle);
>  out_dq:
>         ocfs2_unlock_global_qf(info, 1);
> +out_trans:
> +       ocfs2_commit_trans(osb, handle);
>         if (status < 0)
>                 goto out;