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authorJoe Thornber <ejt@redhat.com>2015-05-15 15:23:35 +0100
committerMike Snitzer <snitzer@redhat.com>2015-05-29 14:19:06 -0400
commit3cdf93f9d85979b22b6abfd4ab19350860e4dfac (patch)
tree4e77c76a3def3bb6aac401047ee7e8566642026a /drivers/md
parent451b9e0071b2833744db7f518115bc085bc7b23c (diff)
downloadop-kernel-dev-3cdf93f9d85979b22b6abfd4ab19350860e4dfac.zip
op-kernel-dev-3cdf93f9d85979b22b6abfd4ab19350860e4dfac.tar.gz
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 <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/dm-bio-prison.c26
-rw-r--r--drivers/md/dm-bio-prison.h13
2 files changed, 39 insertions, 0 deletions
diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
index be06530..cd6d1d2 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 74cf011..54352f0 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);
+
/*----------------------------------------------------------------*/
/*
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