dm: rework queueing and suspension
Rework shutting down on suspend and document the associated rules.
Drop write lock in __split_and_process_bio to allow more processing
concurrency.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index bb97ec8..9746c1e 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1434,18 +1434,21 @@
down_write(&md->io_lock);
- while (1) {
+ while (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
spin_lock_irq(&md->deferred_lock);
c = bio_list_pop(&md->deferred);
spin_unlock_irq(&md->deferred_lock);
if (!c) {
- clear_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
clear_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags);
break;
}
+ up_write(&md->io_lock);
+
__split_and_process_bio(md, c);
+
+ down_write(&md->io_lock);
}
up_write(&md->io_lock);
@@ -1453,8 +1456,9 @@
static void dm_queue_flush(struct mapped_device *md)
{
+ clear_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
+ smp_mb__after_clear_bit();
queue_work(md->wq, &md->work);
- flush_workqueue(md->wq);
}
/*
@@ -1572,22 +1576,36 @@
}
/*
- * First we set the DMF_QUEUE_IO_TO_THREAD flag so no more ios
- * will be mapped.
+ * Here we must make sure that no processes are submitting requests
+ * to target drivers i.e. no one may be executing
+ * __split_and_process_bio. This is called from dm_request and
+ * dm_wq_work.
+ *
+ * To get all processes out of __split_and_process_bio in dm_request,
+ * we take the write lock. To prevent any process from reentering
+ * __split_and_process_bio from dm_request, we set
+ * DMF_QUEUE_IO_TO_THREAD.
+ *
+ * To quiesce the thread (dm_wq_work), we set DMF_BLOCK_IO_FOR_SUSPEND
+ * and call flush_workqueue(md->wq). flush_workqueue will wait until
+ * dm_wq_work exits and DMF_BLOCK_IO_FOR_SUSPEND will prevent any
+ * further calls to __split_and_process_bio from dm_wq_work.
*/
down_write(&md->io_lock);
set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
set_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags);
-
up_write(&md->io_lock);
+ flush_workqueue(md->wq);
+
/*
- * Wait for the already-mapped ios to complete.
+ * At this point no more requests are entering target request routines.
+ * We call dm_wait_for_completion to wait for all existing requests
+ * to finish.
*/
r = dm_wait_for_completion(md, TASK_INTERRUPTIBLE);
down_write(&md->io_lock);
-
if (noflush)
clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);
up_write(&md->io_lock);
@@ -1600,6 +1618,12 @@
goto out; /* pushback list is already flushed, so skip flush */
}
+ /*
+ * If dm_wait_for_completion returned 0, the device is completely
+ * quiescent now. There is no request-processing activity. All new
+ * requests are being added to md->deferred list.
+ */
+
dm_table_postsuspend_targets(map);
set_bit(DMF_SUSPENDED, &md->flags);