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Commit 3cdf93f9 authored by Joe Thornber's avatar Joe Thornber Committed by Mike Snitzer
Browse files

dm bio prison: add dm_cell_promote_or_release() 



Rather than always releasing the prisoners in a cell, the client may
want to promote one of them to be the new holder.  There is a race here
though between releasing an empty cell, and other threads adding new
inmates.  So this function makes the decision with its lock held.

This function can have two outcomes:
i)  An inmate is promoted to be the holder of the cell (return value of 0).
ii) The cell has no inmate for promotion and is released (return value of 1).

Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 451b9e00

drivers/md/dm-bio-prison.c

+26 −0
Original line number Diff line number Diff line
@@ -255,6 +255,32 @@ void dm_cell_visit_release(struct dm_bio_prison *prison, 
}

EXPORT_SYMBOL_GPL(dm_cell_visit_release);



static int __promote_or_release(struct dm_bio_prison *prison,

				struct dm_bio_prison_cell *cell)

{

	if (bio_list_empty(&cell->bios)) {

		rb_erase(&cell->node, &prison->cells);

		return 1;

	}



	cell->holder = bio_list_pop(&cell->bios);

	return 0;

}



int dm_cell_promote_or_release(struct dm_bio_prison *prison,

			       struct dm_bio_prison_cell *cell)

{

	int r;

	unsigned long flags;



	spin_lock_irqsave(&prison->lock, flags);

	r = __promote_or_release(prison, cell);

	spin_unlock_irqrestore(&prison->lock, flags);



	return r;

}

EXPORT_SYMBOL_GPL(dm_cell_promote_or_release);



/*----------------------------------------------------------------*/



#define DEFERRED_SET_SIZE 64

drivers/md/dm-bio-prison.h

+13 −0
Original line number Diff line number Diff line
@@ -101,6 +101,19 @@ void dm_cell_visit_release(struct dm_bio_prison *prison, 
			   void (*visit_fn)(void *, struct dm_bio_prison_cell *),

			   void *context, struct dm_bio_prison_cell *cell);



/*

 * Rather than always releasing the prisoners in a cell, the client may

 * want to promote one of them to be the new holder.  There is a race here

 * though between releasing an empty cell, and other threads adding new

 * inmates.  So this function makes the decision with its lock held.

 *

 * This function can have two outcomes:

 * i) An inmate is promoted to be the holder of the cell (return value of 0).

 * ii) The cell has no inmate for promotion and is released (return value of 1).

 */

int dm_cell_promote_or_release(struct dm_bio_prison *prison,

			       struct dm_bio_prison_cell *cell);



/*----------------------------------------------------------------*/



/*