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Commit 3b00b203 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
Browse files

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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 54d9a1b4

drivers/md/dm.c

+32 −8
Original line number Diff line number Diff line
@@ -1434,18 +1434,21 @@ static void dm_wq_work(struct work_struct *work) 


	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_wq_work(struct work_struct *work) 


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 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) 
	}



	/*

	 * 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 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) 
		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);