linux-kernel - Re: [PATCH v14 13/13] dm: add power-of-2 target for zoned devices with non power-of-2 zone sizes

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Date:   Wed, 21 Sep 2022 19:32:45 +0200
From:   Pankaj Raghav <p.raghav@...sung.com>
To:     Mike Snitzer <snitzer@...hat.com>
CC:     <agk@...hat.com>, <snitzer@...nel.org>, <axboe@...nel.dk>,
        <damien.lemoal@...nsource.wdc.com>, <hch@....de>,
        Damien Le Moal <damien.lemoal@....com>, <bvanassche@....org>,
        <pankydev8@...il.com>, <gost.dev@...sung.com>,
        <linux-kernel@...r.kernel.org>, <linux-nvme@...ts.infradead.org>,
        <linux-block@...r.kernel.org>, <dm-devel@...hat.com>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        <jaegeuk@...nel.org>, <matias.bjorling@....com>
Subject: Re: [PATCH v14 13/13] dm: add power-of-2 target for zoned devices
 with non power-of-2 zone sizes

>> +/*
>> + * This target works on the complete zoned device. Partial mapping is not
>> + * supported.
>> + * Construct a zoned po2 logical device: <dev-path>
>> + */
>> +static int dm_po2z_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>> +{
>> +	struct dm_po2z_target *dmh = NULL;
>> +	int ret;
>> +	sector_t zone_size;
>> +	sector_t dev_capacity;
>> +
>> +	if (argc != 1)
>> +		return -EINVAL;
>> +
>> +	dmh = kmalloc(sizeof(*dmh), GFP_KERNEL);
>> +	if (!dmh)
>> +		return -ENOMEM;
>> +
>> +	ret = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
>> +			    &dmh->dev);
>> +	if (ret) {
>> +		ti->error = "Device lookup failed";
>> +		goto bad;
>> +	}
>> +
>> +	if (!bdev_is_zoned(dmh->dev->bdev)) {
>> +		DMERR("%pg is not a zoned device", dmh->dev->bdev);
>> +		ret = -EINVAL;
>> +		goto bad;
>> +	}
>> +
>> +	zone_size = bdev_zone_sectors(dmh->dev->bdev);
>> +	dev_capacity = get_capacity(dmh->dev->bdev->bd_disk);
>> +	if (ti->len != dev_capacity) {
>> +		DMERR("%pg Partial mapping of the target is not supported",
>> +		      dmh->dev->bdev);
>> +		ret = -EINVAL;
>> +		goto bad;
>> +	}
>> +
>> +	if (is_power_of_2(zone_size))
>> +		DMWARN("%pg: underlying device has a power-of-2 number of sectors per zone",
>> +		       dmh->dev->bdev);
>> +
>> +	dmh->zone_size = zone_size;
>> +	dmh->zone_size_po2 = 1 << get_count_order_long(zone_size);
>> +	dmh->zone_size_po2_shift = ilog2(dmh->zone_size_po2);
>> +	dmh->zone_size_diff = dmh->zone_size_po2 - dmh->zone_size;
>> +	ti->private = dmh;
>> +	ti->max_io_len = dmh->zone_size_po2;
>> +	dmh->nr_zones = npo2_zone_no(dmh, ti->len);
>> +	ti->len = dmh->zone_size_po2 * dmh->nr_zones;
>> +	return 0;
>> +
>> +bad:
>> +	kfree(dmh);
>> +	return ret;
>> +}
> 
> This error handling still isn't correct.  You're using
> dm_get_device().  If you return early due to error, _after_
> dm_get_device(), you need to dm_put_device().
> 
> Basically you need a new label above "bad:" that calls dm_put_device()
> then falls through to "bad:".  Or you need to explcitly call
> dm_put_device() before "goto bad;" in the if (ti->len != dev_capacity)
> error branch.
> 

Ah. I naively assumed dtr will be called to cleanup but not in this case as
the ctr itself fails.

I will add an extra label on top of `bad` and use it for errors that
happens after `dm_get_device`. Thanks for pointing it out Mike.