Commit 7f0e7bed authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

writeback: fix writeback completion notifications 



The code dealing with bdi_work->state and completion of a bdi_work is a
major mess currently.  This patch makes sure we directly use one set of
flags to deal with it, and use it consistently, which means:

 - always notify about completion from the rcu callback.  We only ever
   wait for it from on-stack callers, so this simplification does not
   even cause a theoretical slowdown currently.  It also makes sure we
   don't miss out on the notification if we ever add other callers to
   wait for it.
 - make earlier completion notification depending on the on-stack
   allocation, not the sync mode.  If we introduce new callers that
   want to do WB_SYNC_NONE writeback from on-stack callers this will
   be nessecary.

Also rename bdi_wait_on_work_clear to bdi_wait_on_work_done and inline
a few small functions into their only caller to make the code
understandable.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent 7908a9e5

fs/fs-writeback.c

+15 −50
Original line number Diff line number Diff line
@@ -63,24 +63,16 @@ struct bdi_work { 
};



enum {

	WS_USED_B = 0,

	WS_ONSTACK_B,

	WS_INPROGRESS = 0,

	WS_ONSTACK,

};



#define WS_USED (1 << WS_USED_B)

#define WS_ONSTACK (1 << WS_ONSTACK_B)



static inline bool bdi_work_on_stack(struct bdi_work *work)

{

	return test_bit(WS_ONSTACK_B, &work->state);

}



static inline void bdi_work_init(struct bdi_work *work,

				 struct wb_writeback_args *args)

{

	INIT_RCU_HEAD(&work->rcu_head);

	work->args = *args;

	work->state = WS_USED;

	__set_bit(WS_INPROGRESS, &work->state);

}



/**
@@ -95,43 +87,16 @@ int writeback_in_progress(struct backing_dev_info *bdi) 
	return !list_empty(&bdi->work_list);

}



static void bdi_work_clear(struct bdi_work *work)

{

	clear_bit(WS_USED_B, &work->state);

	smp_mb__after_clear_bit();

	/*

	 * work can have disappeared at this point. bit waitq functions

	 * should be able to tolerate this, provided bdi_sched_wait does

	 * not dereference it's pointer argument.

	*/

	wake_up_bit(&work->state, WS_USED_B);

}



static void bdi_work_free(struct rcu_head *head)

{

	struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);



	if (!bdi_work_on_stack(work))

		kfree(work);

	else

		bdi_work_clear(work);

}



static void wb_work_complete(struct bdi_work *work)

{

	const enum writeback_sync_modes sync_mode = work->args.sync_mode;

	int onstack = bdi_work_on_stack(work);

	clear_bit(WS_INPROGRESS, &work->state);

	smp_mb__after_clear_bit();

	wake_up_bit(&work->state, WS_INPROGRESS);



	/*

	 * For allocated work, we can clear the done/seen bit right here.

	 * For on-stack work, we need to postpone both the clear and free

	 * to after the RCU grace period, since the stack could be invalidated

	 * as soon as bdi_work_clear() has done the wakeup.

	 */

	if (!onstack)

		bdi_work_clear(work);

	if (sync_mode == WB_SYNC_NONE || onstack)

		call_rcu(&work->rcu_head, bdi_work_free);

	if (!test_bit(WS_ONSTACK, &work->state))

		kfree(work);

}



static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
@@ -147,7 +112,7 @@ static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work) 
		list_del_rcu(&work->list);

		spin_unlock(&bdi->wb_lock);



		wb_work_complete(work);

		call_rcu(&work->rcu_head, bdi_work_free);

	}

}
@@ -185,9 +150,9 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work) 
 * Used for on-stack allocated work items. The caller needs to wait until

 * the wb threads have acked the work before it's safe to continue.

 */

static void bdi_wait_on_work_clear(struct bdi_work *work)

static void bdi_wait_on_work_done(struct bdi_work *work)

{

	wait_on_bit(&work->state, WS_USED_B, bdi_sched_wait,

	wait_on_bit(&work->state, WS_INPROGRESS, bdi_sched_wait,

		    TASK_UNINTERRUPTIBLE);

}
@@ -234,10 +199,10 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi, 
	struct bdi_work work;



	bdi_work_init(&work, &args);

	work.state |= WS_ONSTACK;

	__set_bit(WS_ONSTACK, &work.state);



	bdi_queue_work(bdi, &work);

	bdi_wait_on_work_clear(&work);

	bdi_wait_on_work_done(&work);

}



/**
@@ -911,7 +876,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait) 
		 * If this isn't a data integrity operation, just notify

		 * that we have seen this work and we are now starting it.

		 */

		if (args.sync_mode == WB_SYNC_NONE)

		if (!test_bit(WS_ONSTACK, &work->state))

			wb_clear_pending(wb, work);



		wrote += wb_writeback(wb, &args);
@@ -920,7 +885,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait) 
		 * This is a data integrity writeback, so only do the

		 * notification when we have completed the work.

		 */

		if (args.sync_mode == WB_SYNC_ALL)

		if (test_bit(WS_ONSTACK, &work->state))

			wb_clear_pending(wb, work);

	}

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