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

Jan Kara
2024-11-26T09:05:08Z

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

> ---
> 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