Re: [PATCH 5/8] dm: always setup ->orig_bio in alloc_io

Damien Le Moal
2022-04-13T00:00:36Z

On 4/13/22 08:00, Mike Snitzer wrote:
> On Tue, Apr 12 2022 at 6:38P -0400,
> Damien Le Moal <damien.lemoal@opensource.wdc.com> wrote:
>
>> On 4/13/22 05:52, Mike Snitzer wrote:
>>> On Tue, Apr 12 2022 at 4:56P -0400,
>>> Ming Lei <ming.lei@redhat.com> wrote:
>>>
>>>> The current DM codes setup ->orig_bio after __map_bio() returns,
>>>> and not only cause kernel panic for dm zone, but also a bit ugly
>>>> and tricky, especially the waiting until ->orig_bio is set in
>>>> dm_submit_bio_remap().
>>>>
>>>> The reason is that one new bio is cloned from original FS bio to
>>>> represent the mapped part, which just serves io accounting.
>>>>
>>>> Now we have switched to bdev based io accounting interface, and we
>>>> can retrieve sectors/bio_op from both the real original bio and the
>>>> added fields of .sector_offset & .sectors easily, so the new cloned
>>>> bio isn't necessary any more.
>>>>
>>>> Not only fixes dm-zone's kernel panic, but also cleans up dm io
>>>> accounting & split a bit.
>>>
>>> You're conflating quite a few things here. DM zone really has no
>>> business accessing io->orig_bio (dm-zone.c can just as easily inspect
>>> the tio->clone, because it hasn't been remapped yet it reflects the
>>> io->origin_bio, so there is no need to look at io->orig_bio) -- but
>>> yes I clearly broke things during the 5.18 merge and it needs fixing
>>> ASAP.
>>
>> Problem is that we need to look at the BIO op in submission AND completion
>> path to handle zone append requests. So looking at the clone on submission
>> is OK since its op is still the original one. But on the completion path,
>> the clone may now be a regular write emulating a zone append op. And
>> looking at the clone only does not allow detecting that zone append.
>>
>> We could have the orig_bio op saved in dm_io to avoid completely looking
>> at the orig_bio for detecting zone append.
>
> Can you please try the following patch?

This works. I tested with a zoned nullblk + dm-crypt, forcing the zone
append emulation code to be used. I ran zonefs tests on top of that with
no issues. I will run btrfs tests too later today to exercise things a
little more.

>
> Really sorry for breaking dm-zone.c; please teach this man how to test
> the basics of all things dm-zoned (is there a testsuite in the tools
> or something?).
>
> Thanks,
> Mike
>
> diff --git a/drivers/md/dm-zone.c b/drivers/md/dm-zone.c
> index c1ca9be4b79e..896127366000 100644
> --- a/drivers/md/dm-zone.c
> +++ b/drivers/md/dm-zone.c
> @@ -360,16 +360,20 @@ static int dm_update_zone_wp_offset(struct mapped_device *md, unsigned int zno,
> return 0;
> }
>
> +struct orig_bio_details {
> + unsigned int op;
> + unsigned int nr_sectors;
> +};
> +
> /*
> * First phase of BIO mapping for targets with zone append emulation:
> * check all BIO that change a zone writer pointer and change zone
> * append operations into regular write operations.
> */
> -static bool dm_zone_map_bio_begin(struct mapped_device *md,
> - struct bio *orig_bio, struct bio *clone)
> +static bool dm_zone_map_bio_begin(struct mapped_device *md, unsigned int zno,
> + struct bio *clone)
> {
> sector_t zsectors = blk_queue_zone_sectors(md->queue);
> - unsigned int zno = bio_zone_no(orig_bio);
> unsigned int zwp_offset = READ_ONCE(md->zwp_offset[zno]);
>
> /*
> @@ -384,7 +388,7 @@ static bool dm_zone_map_bio_begin(struct mapped_device *md,
> WRITE_ONCE(md->zwp_offset[zno], zwp_offset);
> }
>
> - switch (bio_op(orig_bio)) {
> + switch (bio_op(clone)) {
> case REQ_OP_ZONE_RESET:
> case REQ_OP_ZONE_FINISH:
> return true;
> @@ -401,9 +405,8 @@ static bool dm_zone_map_bio_begin(struct mapped_device *md,
> * target zone.
> */
> clone->bi_opf = REQ_OP_WRITE | REQ_NOMERGE |
> - (orig_bio->bi_opf & (~REQ_OP_MASK));
> - clone->bi_iter.bi_sector =
> - orig_bio->bi_iter.bi_sector + zwp_offset;
> + (clone->bi_opf & (~REQ_OP_MASK));
> + clone->bi_iter.bi_sector += zwp_offset;
> break;
> default:
> DMWARN_LIMIT("Invalid BIO operation");
> @@ -423,11 +426,10 @@ static bool dm_zone_map_bio_begin(struct mapped_device *md,
> * data written to a zone. Note that at this point, the remapped clone BIO
> * may already have completed, so we do not touch it.
> */
> -static blk_status_t dm_zone_map_bio_end(struct mapped_device *md,
> - struct bio *orig_bio,
> +static blk_status_t dm_zone_map_bio_end(struct mapped_device *md, unsigned int zno,
> + struct orig_bio_details *orig_bio_details,
> unsigned int nr_sectors)
> {
> - unsigned int zno = bio_zone_no(orig_bio);
> unsigned int zwp_offset = READ_ONCE(md->zwp_offset[zno]);
>
> /* The clone BIO may already have been completed and failed */
> @@ -435,7 +437,7 @@ static blk_status_t dm_zone_map_bio_end(struct mapped_device *md,
> return BLK_STS_IOERR;
>
> /* Update the zone wp offset */
> - switch (bio_op(orig_bio)) {
> + switch (orig_bio_details->op) {
> case REQ_OP_ZONE_RESET:
> WRITE_ONCE(md->zwp_offset[zno], 0);
> return BLK_STS_OK;
> @@ -452,7 +454,7 @@ static blk_status_t dm_zone_map_bio_end(struct mapped_device *md,
> * Check that the target did not truncate the write operation
> * emulating a zone append.
> */
> - if (nr_sectors != bio_sectors(orig_bio)) {
> + if (nr_sectors != orig_bio_details->nr_sectors) {
> DMWARN_LIMIT("Truncated write for zone append");
> return BLK_STS_IOERR;
> }
> @@ -488,7 +490,7 @@ static inline void dm_zone_unlock(struct request_queue *q,
> bio_clear_flag(clone, BIO_ZONE_WRITE_LOCKED);
> }
>
> -static bool dm_need_zone_wp_tracking(struct bio *orig_bio)
> +static bool dm_need_zone_wp_tracking(struct bio *clone)
> {
> /*
> * Special processing is not needed for operations that do not need the
> @@ -496,15 +498,15 @@ static bool dm_need_zone_wp_tracking(struct bio *orig_bio)
> * zones and all operations that do not modify directly a sequential
> * zone write pointer.
> */
> - if (op_is_flush(orig_bio->bi_opf) && !bio_sectors(orig_bio))
> + if (op_is_flush(clone->bi_opf) && !bio_sectors(clone))
> return false;
> - switch (bio_op(orig_bio)) {
> + switch (bio_op(clone)) {
> case REQ_OP_WRITE_ZEROES:
> case REQ_OP_WRITE:
> case REQ_OP_ZONE_RESET:
> case REQ_OP_ZONE_FINISH:
> case REQ_OP_ZONE_APPEND:
> - return bio_zone_is_seq(orig_bio);
> + return bio_zone_is_seq(clone);
> default:
> return false;
> }
> @@ -519,8 +521,8 @@ int dm_zone_map_bio(struct dm_target_io *tio)
> struct dm_target *ti = tio->ti;
> struct mapped_device *md = io->md;
> struct request_queue *q = md->queue;
> - struct bio *orig_bio = io->orig_bio;
> struct bio *clone = &tio->clone;
> + struct orig_bio_details orig_bio_details;
> unsigned int zno;
> blk_status_t sts;
> int r;
> @@ -529,18 +531,21 @@ int dm_zone_map_bio(struct dm_target_io *tio)
> * IOs that do not change a zone write pointer do not need
> * any additional special processing.
> */
> - if (!dm_need_zone_wp_tracking(orig_bio))
> + if (!dm_need_zone_wp_tracking(clone))
> return ti->type->map(ti, clone);
>
> /* Lock the target zone */
> - zno = bio_zone_no(orig_bio);
> + zno = bio_zone_no(clone);
> dm_zone_lock(q, zno, clone);
>
> + orig_bio_details.nr_sectors = bio_sectors(clone);
> + orig_bio_details.op = bio_op(clone);
> +
> /*
> * Check that the bio and the target zone write pointer offset are
> * both valid, and if the bio is a zone append, remap it to a write.
> */
> - if (!dm_zone_map_bio_begin(md, orig_bio, clone)) {
> + if (!dm_zone_map_bio_begin(md, zno, clone)) {
> dm_zone_unlock(q, zno, clone);
> return DM_MAPIO_KILL;
> }
> @@ -560,7 +565,8 @@ int dm_zone_map_bio(struct dm_target_io *tio)
> * The target submitted the clone BIO. The target zone will
> * be unlocked on completion of the clone.
> */
> - sts = dm_zone_map_bio_end(md, orig_bio, *tio->len_ptr);
> + sts = dm_zone_map_bio_end(md, zno, &orig_bio_details,
> + *tio->len_ptr);
> break;
> case DM_MAPIO_REMAPPED:
> /*
> @@ -568,7 +574,8 @@ int dm_zone_map_bio(struct dm_target_io *tio)
> * unlock the target zone here as the clone will not be
> * submitted.
> */
> - sts = dm_zone_map_bio_end(md, orig_bio, *tio->len_ptr);
> + sts = dm_zone_map_bio_end(md, zno, &orig_bio_details,
> + *tio->len_ptr);
> if (sts != BLK_STS_OK)
> dm_zone_unlock(q, zno, clone);
> break;
>

--
Damien Le Moal
Western Digital Research