From 3cdf93f9d85979b22b6abfd4ab19350860e4dfac Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Fri, 15 May 2015 15:23:35 +0100 Subject: [PATCH] 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: Joe Thornber Signed-off-by: Mike Snitzer --- drivers/md/dm-bio-prison.c | 26 ++++++++++++++++++++++++++ drivers/md/dm-bio-prison.h | 13 +++++++++++++ 2 files changed, 39 insertions(+) diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c index be065300e93c..cd6d1d21e057 100644 --- a/drivers/md/dm-bio-prison.c +++ b/drivers/md/dm-bio-prison.c @@ -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 diff --git a/drivers/md/dm-bio-prison.h b/drivers/md/dm-bio-prison.h index 74cf01144b1f..54352f009bfd 100644 --- a/drivers/md/dm-bio-prison.h +++ b/drivers/md/dm-bio-prison.h @@ -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); + /*----------------------------------------------------------------*/ /*