[PATCH] dm snapshot: add workqueue

Add a workqueue so that I/O can be queued up to be flushed from a separate
thread (e.g.  if local interrupts are disabled).

A new per-snapshot spinlock pe_lock is introduced to protect queued_bios.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 45 insertions, 0 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index d92980177b5c..1c6485404db4 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -39,6 +39,9 @@
  */
 #define SNAPSHOT_PAGES 256
 
+struct workqueue_struct *ksnapd;
+static void flush_queued_bios(void *data);
+
 struct pending_exception {
         struct exception e;
 
@@ -488,6 +491,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
         s->active = 0;
         s->last_percent = 0;
         init_rwsem(&s->lock);
+        spin_lock_init(&s->pe_lock);
         s->table = ti->table;
 
         /* Allocate hash table for COW data */
@@ -523,6 +527,9 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
                 goto bad6;
         }
 
+        bio_list_init(&s->queued_bios);
+        INIT_WORK(&s->queued_bios_work, flush_queued_bios, s);
+
         /* Add snapshot to the list of snapshots for this origin */
         /* Exceptions aren't triggered till snapshot_resume() is called */
         if (register_snapshot(s)) {
@@ -561,6 +568,8 @@ static void snapshot_dtr(struct dm_target *ti)
 {
         struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
 
+        flush_workqueue(ksnapd);
+
         /* Prevent further origin writes from using this snapshot. */
         /* After this returns there can be no new kcopyd jobs. */
         unregister_snapshot(s);
@@ -594,6 +603,19 @@ static void flush_bios(struct bio *bio)
         }
 }
 
+static void flush_queued_bios(void *data)
+{
+        struct dm_snapshot *s = (struct dm_snapshot *) data;
+        struct bio *queued_bios;
+        unsigned long flags;
+
+        spin_lock_irqsave(&s->pe_lock, flags);
+        queued_bios = bio_list_get(&s->queued_bios);
+        spin_unlock_irqrestore(&s->pe_lock, flags);
+
+        flush_bios(queued_bios);
+}
+
 /*
  * Error a list of buffers.
  */
@@ -1240,8 +1262,17 @@ static int __init dm_snapshot_init(void)
                 goto bad5;
         }
 
+        ksnapd = create_singlethread_workqueue("ksnapd");
+        if (!ksnapd) {
+                DMERR("Failed to create ksnapd workqueue.");
+                r = -ENOMEM;
+                goto bad6;
+        }
+
         return 0;
 
+      bad6:
+        mempool_destroy(pending_pool);
       bad5:
         kmem_cache_destroy(pending_cache);
       bad4:
@@ -1259,6 +1290,8 @@ static void __exit dm_snapshot_exit(void)
 {
         int r;
 
+        destroy_workqueue(ksnapd);
+
         r = dm_unregister_target(&snapshot_target);
         if (r)
                 DMERR("snapshot unregister failed %d", r);
diff --git a/drivers/md/dm-snap.h b/drivers/md/dm-snap.h
index 221eb8880c80..15fa2ae6cdc2 100644
--- a/drivers/md/dm-snap.h
+++ b/drivers/md/dm-snap.h
@@ -10,7 +10,9 @@
 #define DM_SNAPSHOT_H
 
 #include "dm.h"
+#include "dm-bio-list.h"
 #include <linux/blkdev.h>
+#include <linux/workqueue.h>
 
 struct exception_table {
         uint32_t hash_mask;
@@ -112,10 +114,20 @@ struct dm_snapshot {
         struct exception_table pending;
         struct exception_table complete;
 
+        /*
+         * pe_lock protects all pending_exception operations and access
+         * as well as the snapshot_bios list.
+         */
+        spinlock_t pe_lock;
+
         /* The on disk metadata handler */
         struct exception_store store;
 
         struct kcopyd_client *kcopyd_client;
+
+        /* Queue of snapshot writes for ksnapd to flush */
+        struct bio_list queued_bios;
+        struct work_struct queued_bios_work;
 };
 
 /*