dm: set the static flush bio device on demand (892ad71f) · Commits · 戴 / test

The next patch changes the macro bio_set_dev() to associate a bio with a blkg based on the device set. However, dm creates a static bio to be used as the basis for cloning empty flush bios on creation. The bio_set_dev() call in alloc_dev() will cause problems with the next patch adding association to bio_set_dev() because the call is before the bdev is associated with a gendisk (bd_disk is %NULL). To get around this, set the device on the static bio every time and use that to clone to the other bios. Signed-off-by:

Dennis Zhou <dennis@kernel.org> Acked-by:

Mike Snitzer <snitzer@redhat.com> Cc: Alasdair Kergon <agk@redhat.com> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

block/bio.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -2021,6 +2021,7 @@ void bio_disassociate_blkg(struct bio *bio)
		bio->bi_blkg = NULL;
		}
		}
		EXPORT_SYMBOL_GPL(bio_disassociate_blkg);

		/**
		* __bio_associate_blkg - associate a bio with the a blkg

drivers/md/dm.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -1417,10 +1417,21 @@ static int __send_empty_flush(struct clone_info *ci)
		unsigned target_nr = 0;
		struct dm_target *ti;

		/*
		* Empty flush uses a statically initialized bio, &md->flush_bio, as
		* the base for cloning. However, blkg association requires that a
		* bdev is associated with a gendisk, which doesn't happen until the
		* bdev is opened. So, blkg association is done at issue time of the
		* flush rather than when the device is created in alloc_dev().
		*/
		bio_set_dev(ci->bio, ci->io->md->bdev);

		BUG_ON(bio_has_data(ci->bio));
		while ((ti = dm_table_get_target(ci->map, target_nr++)))
		__send_duplicate_bios(ci, ti, ti->num_flush_bios, NULL);

		bio_disassociate_blkg(ci->bio);

		return 0;
		}

		@@ -1939,7 +1950,6 @@ static struct mapped_device *alloc_dev(int minor)
		goto bad;

		bio_init(&md->flush_bio, NULL, 0);
		bio_set_dev(&md->flush_bio, md->bdev);
		md->flush_bio.bi_opf = REQ_OP_WRITE \| REQ_PREFLUSH \| REQ_SYNC;

		dm_stats_init(&md->stats);

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