blockjob: add .clean property

Cleaning up after we have deferred to the main thread but before the
transaction has converged can be dangerous and result in deadlocks
if the job cleanup invokes any BH polling loops.

A job may attempt to begin cleaning up, but may induce another job to
enter its cleanup routine. The second job, part of our same transaction,
will block waiting for the first job to finish, so neither job may now
make progress.

To rectify this, allow jobs to register a cleanup operation that will
always run regardless of if the job was in a transaction or not, and
if the transaction job group completed successfully or not.

Move sensitive cleanup to this callback instead which is guaranteed to
be run only after the transaction has converged, which removes sensitive
timing constraints from said cleanup.

Furthermore, in future patches these cleanup operations will be performed
regardless of whether or not we actually started the job. Therefore,
cleanup callbacks should essentially confine themselves to undoing create
operations, e.g. setup actions taken in what is now backup_start.

Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1478587839-9834-3-git-send-email-jsnow@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>

diff --git a/block/backup.c b/block/backup.c
index 7b5d8a3757d3d28cab42b9a145af9b7c70c3f8cc..734a24c69840f036fb743721dc7c764c3ec9e8b9 100644 (file)
--- a/block/backup.c
+++ b/block/backup.c
@@ -242,6 +242,14 @@ static void backup_abort(BlockJob *job)
     }
 }
 
+static void backup_clean(BlockJob *job)
+{
+    BackupBlockJob *s = container_of(job, BackupBlockJob, common);
+    assert(s->target);
+    blk_unref(s->target);
+    s->target = NULL;
+}
+
 static void backup_attached_aio_context(BlockJob *job, AioContext *aio_context)
 {
     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
@@ -321,6 +329,7 @@ static const BlockJobDriver backup_job_driver = {
     .set_speed              = backup_set_speed,
     .commit                 = backup_commit,
     .abort                  = backup_abort,
+    .clean                  = backup_clean,
     .attached_aio_context   = backup_attached_aio_context,
     .drain                  = backup_drain,
 };
@@ -343,12 +352,8 @@ typedef struct {
 
 static void backup_complete(BlockJob *job, void *opaque)
 {
-    BackupBlockJob *s = container_of(job, BackupBlockJob, common);
     BackupCompleteData *data = opaque;
 
-    blk_unref(s->target);
-    s->target = NULL;
-
     block_job_completed(job, data->ret);
     g_free(data);
 }
@@ -658,7 +663,7 @@ void backup_start(const char *job_id, BlockDriverState *bs,
         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
     }
     if (job) {
-        blk_unref(job->target);
+        backup_clean(&job->common);
         block_job_unref(&job->common);
     }
 }

diff --git a/blockjob.c b/blockjob.c
index 4d0ef53fba931b2958d153cb2100f57d482d1017..e3c458c021b173d422db2cb1033dd712d74e4f59 100644 (file)
--- a/blockjob.c
+++ b/blockjob.c
@@ -241,6 +241,9 @@ static void block_job_completed_single(BlockJob *job)
             job->driver->abort(job);
         }
     }
+    if (job->driver->clean) {
+        job->driver->clean(job);
+    }
 
     if (job->cb) {
         job->cb(job->opaque, job->ret);

diff --git a/include/block/blockjob_int.h b/include/block/blockjob_int.h
index 40275e44374691969629013d247107f01c927147..60d91a06786459ceeb5516289e548a30b0403191 100644 (file)
--- a/include/block/blockjob_int.h
+++ b/include/block/blockjob_int.h
@@ -73,6 +73,14 @@ struct BlockJobDriver {
      */
     void (*abort)(BlockJob *job);
 
+    /**
+     * If the callback is not NULL, it will be invoked after a call to either
+     * .commit() or .abort(). Regardless of which callback is invoked after
+     * completion, .clean() will always be called, even if the job does not
+     * belong to a transaction group.
+     */
+    void (*clean)(BlockJob *job);
+
     /**
      * If the callback is not NULL, it will be invoked when the job transitions
      * into the paused state.  Paused jobs must not perform any asynchronous