dm: report suspended device during destroy

The function dm_suspended returns true if the target is suspended.
However, when the target is being suspended during unload, it returns
false.

An example where this is a problem: the test "!dm_suspended(wc->ti)" in
writecache_writeback is not sufficient, because dm_suspended returns
zero while writecache_suspend is in progress.  As is, without an
enhanced dm_suspended, simply switching from flush_workqueue to
drain_workqueue still emits warnings:
workqueue writecache-writeback: drain_workqueue() isn't complete after 10 tries
workqueue writecache-writeback: drain_workqueue() isn't complete after 100 tries
workqueue writecache-writeback: drain_workqueue() isn't complete after 200 tries
workqueue writecache-writeback: drain_workqueue() isn't complete after 300 tries
workqueue writecache-writeback: drain_workqueue() isn't complete after 400 tries

writecache_suspend calls flush_workqueue(wc->writeback_wq) - this function
flushes the current work. However, the workqueue may re-queue itself and
flush_workqueue doesn't wait for re-queued works to finish. Because of
this - the function writecache_writeback continues execution after the
device was suspended and then concurrently with writecache_dtr, causing
a crash in writecache_writeback.

We must use drain_workqueue - that waits until the work and all re-queued
works finish.

As a prereq for switching to drain_workqueue, this commit fixes
dm_suspended to return true after the presuspend hook and before the
postsuspend hook - just like during a normal suspend. It allows
simplifying the dm-integrity and dm-writecache targets so that they
don't have to maintain suspended flags on their own.

With this change use of drain_workqueue() can be used effectively.  This
change was tested with the lvm2 testsuite and cryptsetup testsuite and
the are no regressions.

Fixes: 48debafe ("dm: add writecache target")
Cc: stable@vger.kernel.org # 4.18+
Reported-by: Corey Marthaler <cmarthal@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-integrity.c

@@ -201,12 +201,13 @@ struct dm_integrity_c {
 	__u8 log2_blocks_per_bitmap_bit;
 
 	unsigned char mode;
-	int suspending;
 
 	int failed;
 
 	struct crypto_shash *internal_hash;
 
+	struct dm_target *ti;
+
 	/* these variables are locked with endio_wait.lock */
 	struct rb_root in_progress;
 	struct list_head wait_list;
@@ -2316,7 +2317,7 @@ static void integrity_writer(struct work_struct *w)
 	unsigned prev_free_sectors;
 
 	/* the following test is not needed, but it tests the replay code */
-	if (READ_ONCE(ic->suspending) && !ic->meta_dev)
+	if (unlikely(dm_suspended(ic->ti)) && !ic->meta_dev)
 		return;
 
 	spin_lock_irq(&ic->endio_wait.lock);
@@ -2377,7 +2378,7 @@ static void integrity_recalc(struct work_struct *w)
 
 next_chunk:
 
-	if (unlikely(READ_ONCE(ic->suspending)))
+	if (unlikely(dm_suspended(ic->ti)))
 		goto unlock_ret;
 
 	range.logical_sector = le64_to_cpu(ic->sb->recalc_sector);
@@ -2805,8 +2806,6 @@ static void dm_integrity_postsuspend(struct dm_target *ti)
 
 	del_timer_sync(&ic->autocommit_timer);
 
-	WRITE_ONCE(ic->suspending, 1);
-
 	if (ic->recalc_wq)
 		drain_workqueue(ic->recalc_wq);
 
@@ -2835,8 +2834,6 @@ static void dm_integrity_postsuspend(struct dm_target *ti)
 #endif
 	}
 
-	WRITE_ONCE(ic->suspending, 0);
-
 	BUG_ON(!RB_EMPTY_ROOT(&ic->in_progress));
 
 	ic->journal_uptodate = true;
@@ -3631,6 +3628,7 @@ static int dm_integrity_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	}
 	ti->private = ic;
 	ti->per_io_data_size = sizeof(struct dm_integrity_io);
+	ic->ti = ti;
 
 	ic->in_progress = RB_ROOT;
 	INIT_LIST_HEAD(&ic->wait_list);

drivers/md/dm-writecache.c

@@ -842,7 +842,7 @@ static void writecache_suspend(struct dm_target *ti)
 	}
 	wc_unlock(wc);
 
-	flush_workqueue(wc->writeback_wq);
+	drain_workqueue(wc->writeback_wq);
 
 	wc_lock(wc);
 	if (flush_on_suspend)

drivers/md/dm.c

@@ -2368,6 +2368,7 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
 	map = dm_get_live_table(md, &srcu_idx);
 	if (!dm_suspended_md(md)) {
 		dm_table_presuspend_targets(map);
+		set_bit(DMF_SUSPENDED, &md->flags);
 		dm_table_postsuspend_targets(map);
 	}
 	/* dm_put_live_table must be before msleep, otherwise deadlock is possible */