drbd: Clarify when activity log I/O is delegated to the worker thread

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

5 files changed, 31 insertions, 26 deletions

diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index c79625aa8cf2..82199d9a9a61 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -104,7 +104,7 @@ struct update_al_work {
         int err;
 };
 
-static int al_write_transaction(struct drbd_conf *mdev);
+static int al_write_transaction(struct drbd_conf *mdev, bool delegate);
 
 void *drbd_md_get_buffer(struct drbd_conf *mdev)
 {
@@ -246,7 +246,10 @@ static struct lc_element *_al_get(struct drbd_conf *mdev, unsigned int enr)
         return al_ext;
 }
 
-void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i)
+/*
+ * @delegate:   delegate activity log I/O to the worker thread
+ */
+void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool delegate)
 {
         /* for bios crossing activity log extent boundaries,
          * we may need to activate two extents in one go */
@@ -255,6 +258,17 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i)
         unsigned enr;
         bool locked = false;
 
+        /* When called through generic_make_request(), we must delegate
+         * activity log I/O to the worker thread: a further request
+         * submitted via generic_make_request() within the same task
+         * would be queued on current->bio_list, and would only start
+         * after this function returns (see generic_make_request()).
+         *
+         * However, if we *are* the worker, we must not delegate to ourselves.
+         */
+
+        if (delegate)
+                BUG_ON(current == mdev->tconn->worker.task);
 
         D_ASSERT(first <= last);
         D_ASSERT(atomic_read(&mdev->local_cnt) > 0);
@@ -270,13 +284,6 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i)
                         (locked = lc_try_lock_for_transaction(mdev->act_log)));
 
         if (locked) {
-                /* drbd_al_write_transaction(mdev,al_ext,enr);
-                 * recurses into generic_make_request(), which
-                 * disallows recursion, bios being serialized on the
-                 * current->bio_tail list now.
-                 * we have to delegate updates to the activity log
-                 * to the worker thread. */
-
                 /* Double check: it may have been committed by someone else,
                  * while we have been waiting for the lock. */
                 if (mdev->act_log->pending_changes) {
@@ -287,7 +294,7 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i)
                         rcu_read_unlock();
 
                         if (write_al_updates) {
-                                al_write_transaction(mdev);
+                                al_write_transaction(mdev, delegate);
                                 mdev->al_writ_cnt++;
                         }
 
@@ -495,20 +502,18 @@ static int w_al_write_transaction(struct drbd_work *w, int unused)
 /* Calls from worker context (see w_restart_disk_io()) need to write the
    transaction directly. Others came through generic_make_request(),
    those need to delegate it to the worker. */
-static int al_write_transaction(struct drbd_conf *mdev)
+static int al_write_transaction(struct drbd_conf *mdev, bool delegate)
 {
-        struct update_al_work al_work;
-
-        if (current == mdev->tconn->worker.task)
+        if (delegate) {
+                struct update_al_work al_work;
+                init_completion(&al_work.event);
+                al_work.w.cb = w_al_write_transaction;
+                al_work.w.mdev = mdev;
+                drbd_queue_work_front(&mdev->tconn->sender_work, &al_work.w);
+                wait_for_completion(&al_work.event);
+                return al_work.err;
+        } else
                 return _al_write_transaction(mdev);
-
-        init_completion(&al_work.event);
-        al_work.w.cb = w_al_write_transaction;
-        al_work.w.mdev = mdev;
-        drbd_queue_work_front(&mdev->tconn->sender_work, &al_work.w);
-        wait_for_completion(&al_work.event);
-
-        return al_work.err;
 }
 
 static int _try_lc_del(struct drbd_conf *mdev, struct lc_element *al_ext)
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 6eecdec9da2b..453fccfc440c 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -1598,7 +1598,7 @@ extern const char *drbd_conn_str(enum drbd_conns s);
 extern const char *drbd_role_str(enum drbd_role s);
 
 /* drbd_actlog.c */
-extern void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i);
+extern void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool delegate);
 extern void drbd_al_complete_io(struct drbd_conf *mdev, struct drbd_interval *i);
 extern void drbd_rs_complete_io(struct drbd_conf *mdev, sector_t sector);
 extern int drbd_rs_begin_io(struct drbd_conf *mdev, sector_t sector);
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 8172a2cfdead..1921871ca9a8 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -2265,7 +2265,7 @@ static int receive_Data(struct drbd_tconn *tconn, struct packet_info *pi)
                 drbd_set_out_of_sync(mdev, peer_req->i.sector, peer_req->i.size);
                 peer_req->flags |= EE_CALL_AL_COMPLETE_IO;
                 peer_req->flags &= ~EE_MAY_SET_IN_SYNC;
-                drbd_al_begin_io(mdev, &peer_req->i);
+                drbd_al_begin_io(mdev, &peer_req->i, true);
         }
 
         err = drbd_submit_peer_request(mdev, peer_req, rw, DRBD_FAULT_DT_WR);
diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 2b8303ad63c9..7d1ff1aaeb71 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -1054,7 +1054,7 @@ void __drbd_make_request(struct drbd_conf *mdev, struct bio *bio, unsigned long
         if (rw == WRITE && req->private_bio && req->i.size
         && !test_bit(AL_SUSPENDED, &mdev->flags)) {
                 req->rq_state |= RQ_IN_ACT_LOG;
-                drbd_al_begin_io(mdev, &req->i);
+                drbd_al_begin_io(mdev, &req->i, true);
         }
 
         spin_lock_irq(&mdev->tconn->req_lock);
diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 34b5d5d23ac4..f41e224caa7c 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -1411,7 +1411,7 @@ int w_restart_disk_io(struct drbd_work *w, int cancel)
         struct drbd_conf *mdev = w->mdev;
 
         if (bio_data_dir(req->master_bio) == WRITE && req->rq_state & RQ_IN_ACT_LOG)
-                drbd_al_begin_io(mdev, &req->i);
+                drbd_al_begin_io(mdev, &req->i, false);
 
         drbd_req_make_private_bio(req, req->master_bio);
         req->private_bio->bi_bdev = mdev->ldev->backing_bdev;