[PATCH] dm snapshot: fix kcopyd destructor

Before removing a snapshot, wait for the completion of any kcopyd jobs using
it.

Do this by maintaining a count (nr_jobs) of how many outstanding jobs each
kcopyd_client has.

The snapshot destructor first unregisters the snapshot so that no new kcopyd
jobs (created by writes to the origin) will reference that particular
snapshot.  kcopyd_client_destroy() is now run next to wait for the completion
of any outstanding jobs before the snapshot exception structures (that those
jobs reference) are freed.

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

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index a5765f9..08312b4 100644 (file)
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -559,8 +559,12 @@ static void snapshot_dtr(struct dm_target *ti)
 {
        struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
 
+       /* Prevent further origin writes from using this snapshot. */
+       /* After this returns there can be no new kcopyd jobs. */
        unregister_snapshot(s);
 
+       kcopyd_client_destroy(s->kcopyd_client);
+
        exit_exception_table(&s->pending, pending_cache);
        exit_exception_table(&s->complete, exception_cache);
 
@@ -569,7 +573,7 @@ static void snapshot_dtr(struct dm_target *ti)
 
        dm_put_device(ti, s->origin);
        dm_put_device(ti, s->cow);
-       kcopyd_client_destroy(s->kcopyd_client);
+
        kfree(s);
 }
 

diff --git a/drivers/md/kcopyd.c b/drivers/md/kcopyd.c
index 9dcb2c8..ed71f3f 100644 (file)
--- a/drivers/md/kcopyd.c
+++ b/drivers/md/kcopyd.c
@@ -44,6 +44,9 @@ struct kcopyd_client {
        struct page_list *pages;
        unsigned int nr_pages;
        unsigned int nr_free_pages;
+
+       wait_queue_head_t destroyq;
+       atomic_t nr_jobs;
 };
 
 static struct page_list *alloc_pl(void)
@@ -292,10 +295,15 @@ static int run_complete_job(struct kcopyd_job *job)
        int read_err = job->read_err;
        unsigned int write_err = job->write_err;
        kcopyd_notify_fn fn = job->fn;
+       struct kcopyd_client *kc = job->kc;
 
-       kcopyd_put_pages(job->kc, job->pages);
+       kcopyd_put_pages(kc, job->pages);
        mempool_free(job, _job_pool);
        fn(read_err, write_err, context);
+
+       if (atomic_dec_and_test(&kc->nr_jobs))
+               wake_up(&kc->destroyq);
+
        return 0;
 }
 
@@ -430,6 +438,7 @@ static void do_work(void *ignored)
  */
 static void dispatch_job(struct kcopyd_job *job)
 {
+       atomic_inc(&job->kc->nr_jobs);
        push(&_pages_jobs, job);
        wake();
 }
@@ -669,6 +678,9 @@ int kcopyd_client_create(unsigned int nr_pages, struct kcopyd_client **result)
                return r;
        }
 
+       init_waitqueue_head(&kc->destroyq);
+       atomic_set(&kc->nr_jobs, 0);
+
        client_add(kc);
        *result = kc;
        return 0;
@@ -676,6 +688,9 @@ int kcopyd_client_create(unsigned int nr_pages, struct kcopyd_client **result)
 
 void kcopyd_client_destroy(struct kcopyd_client *kc)
 {
+       /* Wait for completion of all jobs submitted by this client. */
+       wait_event(kc->destroyq, !atomic_read(&kc->nr_jobs));
+
        dm_io_put(kc->nr_pages);
        client_free_pages(kc);
        client_del(kc);