dm: simplify dm_sumbit_bio_remap interface

Remove the from_wq argument from dm_sumbit_bio_remap(). Eliminates the
need for dm_sumbit_bio_remap() callers to know whether they are
calling for a workqueue or from the original dm_submit_bio().

Add map_task to dm_io struct, record the map_task in alloc_io and
clear it after all target ->map() calls have completed. Update
dm_sumbit_bio_remap to check if 'current' matches io->map_task rather
than rely on passed 'from_rq' argument.

This change really simplifies the chore of porting each DM target to
using dm_sumbit_bio_remap() because there is no longer the risk of
programming error by not completely knowing all the different contexts
a particular method that calls dm_sumbit_bio_remap() might be used in.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-core.h

@@ -237,6 +237,7 @@ struct dm_io {
 	unsigned long start_time;
 	void *data;
 	struct hlist_node node;
+	struct task_struct *map_task;
 	spinlock_t endio_lock;
 	struct dm_stats_aux stats_aux;
 	/* last member of dm_target_io is 'struct bio' */

drivers/md/dm-crypt.c

@@ -1857,7 +1857,7 @@ static int kcryptd_io_read(struct dm_crypt_io *io, gfp_t gfp)
 		return 1;
 	}
 
-	dm_submit_bio_remap(io->base_bio, clone, (gfp != CRYPT_MAP_READ_GFP));
+	dm_submit_bio_remap(io->base_bio, clone);
 	return 0;
 }
 
@@ -1883,7 +1883,7 @@ static void kcryptd_io_write(struct dm_crypt_io *io)
 {
 	struct bio *clone = io->ctx.bio_out;
 
-	dm_submit_bio_remap(io->base_bio, clone, true);
+	dm_submit_bio_remap(io->base_bio, clone);
 }
 
 #define crypt_io_from_node(node) rb_entry((node), struct dm_crypt_io, rb_node)
@@ -1962,7 +1962,7 @@ static void kcryptd_crypt_write_io_submit(struct dm_crypt_io *io, int async)
 
 	if ((likely(!async) && test_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags)) ||
 	    test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags)) {
-		dm_submit_bio_remap(io->base_bio, clone, true);
+		dm_submit_bio_remap(io->base_bio, clone);
 		return;
 	}
 

drivers/md/dm-delay.c

@@ -72,7 +72,7 @@ static void flush_bios(struct bio *bio)
 	while (bio) {
 		n = bio->bi_next;
 		bio->bi_next = NULL;
-		dm_submit_bio_remap(bio, NULL, true);
+		dm_submit_bio_remap(bio, NULL);
 		bio = n;
 	}
 }

drivers/md/dm-thin.c

@@ -755,7 +755,7 @@ static void issue(struct thin_c *tc, struct bio *bio)
 	struct pool *pool = tc->pool;
 
 	if (!bio_triggers_commit(tc, bio)) {
-		dm_submit_bio_remap(bio, NULL, true);
+		dm_submit_bio_remap(bio, NULL);
 		return;
 	}
 
@@ -2383,7 +2383,7 @@ static void process_deferred_bios(struct pool *pool)
 		if (bio->bi_opf & REQ_PREFLUSH)
 			bio_endio(bio);
 		else
-			dm_submit_bio_remap(bio, NULL, true);
+			dm_submit_bio_remap(bio, NULL);
 	}
 }
 

drivers/md/dm.c

@@ -574,6 +574,7 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio)
 	this_cpu_inc(*md->pending_io);
 	io->orig_bio = NULL;
 	io->md = md;
+	io->map_task = current;
 	spin_lock_init(&io->endio_lock);
 
 	io->start_time = jiffies;
@@ -1189,15 +1190,13 @@ static inline void __dm_submit_bio_remap(struct bio *clone,
 /*
  * @clone: clone bio that DM core passed to target's .map function
  * @tgt_clone: clone of @clone bio that target needs submitted
- * @from_wq: caller is a workqueue thread managed by DM target
  *
  * Targets should use this interface to submit bios they take
  * ownership of when returning DM_MAPIO_SUBMITTED.
  *
  * Target should also enable ti->accounts_remapped_io
  */
-void dm_submit_bio_remap(struct bio *clone, struct bio *tgt_clone,
-			 bool from_wq)
+void dm_submit_bio_remap(struct bio *clone, struct bio *tgt_clone)
 {
 	struct dm_target_io *tio = clone_to_tio(clone);
 	struct dm_io *io = tio->io;
@@ -1212,7 +1211,7 @@ void dm_submit_bio_remap(struct bio *clone, struct bio *tgt_clone,
 	 * Account io->origin_bio to DM dev on behalf of target
 	 * that took ownership of IO with DM_MAPIO_SUBMITTED.
 	 */
-	if (!from_wq) {
+	if (io->map_task == current) {
 		/* Still in target's map function */
 		io->start_io_acct = true;
 	} else {
@@ -1568,6 +1567,7 @@ static void dm_split_and_process_bio(struct mapped_device *md,
 	}
 
 	error = __split_and_process_bio(&ci);
+	ci.io->map_task = NULL;
 	if (error || !ci.sector_count)
 		goto out;
 

include/linux/device-mapper.h

@@ -471,7 +471,7 @@ int dm_suspended(struct dm_target *ti);
 int dm_post_suspending(struct dm_target *ti);
 int dm_noflush_suspending(struct dm_target *ti);
 void dm_accept_partial_bio(struct bio *bio, unsigned n_sectors);
-void dm_submit_bio_remap(struct bio *clone, struct bio *tgt_clone, bool from_wq);
+void dm_submit_bio_remap(struct bio *clone, struct bio *tgt_clone);
 union map_info *dm_get_rq_mapinfo(struct request *rq);
 
 #ifdef CONFIG_BLK_DEV_ZONED