drbd: Removed a race that could cause unexpected execution of w_make_resync_request()

The actual race happened int the drbd_start_resync() function. Where
drbd_resync_finished() -> __drbd_set_state() set STOP_SYNC_TIMER and
armed the timer.

If the timer fired before execution reaches the mod_timer statement
at the end of drbd_start_resync() the latter would cause an
unexpected call to w_make_resync_request().

Removed the STOP_SYNC_TIMER bit, and base it on the connection state.

The STOP_SYNC_TIMER bit probably originates probably the time before
the state engine.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

4 files changed, 11 insertions, 30 deletions

diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index bb3a488b6fd6..d5e38de83a19 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -827,7 +827,6 @@ enum {
         SIGNAL_ASENDER,         /* whether asender wants to be interrupted */
         SEND_PING,              /* whether asender should send a ping asap */
 
-        STOP_SYNC_TIMER,        /* tell timer to cancel itself */
         UNPLUG_QUEUED,          /* only relevant with kernel 2.4 */
         UNPLUG_REMOTE,          /* sending a "UnplugRemote" could help */
         MD_DIRTY,               /* current uuids and flags not yet on disk */
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 73c905d0ef18..5dd071e5c921 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -1052,12 +1052,6 @@ int __drbd_set_state(struct drbd_conf *mdev,
         wake_up(&mdev->misc_wait);
         wake_up(&mdev->state_wait);
 
-        /*   post-state-change actions   */
-        if (os.conn >= C_SYNC_SOURCE   && ns.conn <= C_CONNECTED) {
-                set_bit(STOP_SYNC_TIMER, &mdev->flags);
-                mod_timer(&mdev->resync_timer, jiffies);
-        }
-
         /* aborted verify run. log the last position */
         if ((os.conn == C_VERIFY_S || os.conn == C_VERIFY_T) &&
             ns.conn < C_CONNECTED) {
@@ -1072,22 +1066,14 @@ int __drbd_set_state(struct drbd_conf *mdev,
                 dev_info(DEV, "Syncer continues.\n");
                 mdev->rs_paused += (long)jiffies
                                   -(long)mdev->rs_mark_time[mdev->rs_last_mark];
-                if (ns.conn == C_SYNC_TARGET) {
-                        if (!test_and_clear_bit(STOP_SYNC_TIMER, &mdev->flags))
-                                mod_timer(&mdev->resync_timer, jiffies);
-                        /* This if (!test_bit) is only needed for the case
-                           that a device that has ceased to used its timer,
-                           i.e. it is already in drbd_resync_finished() gets
-                           paused and resumed. */
-                }
+                if (ns.conn == C_SYNC_TARGET)
+                        mod_timer(&mdev->resync_timer, jiffies);
         }
 
         if ((os.conn == C_SYNC_TARGET  || os.conn == C_SYNC_SOURCE) &&
             (ns.conn == C_PAUSED_SYNC_T || ns.conn == C_PAUSED_SYNC_S)) {
                 dev_info(DEV, "Resync suspended\n");
                 mdev->rs_mark_time[mdev->rs_last_mark] = jiffies;
-                if (ns.conn == C_PAUSED_SYNC_T)
-                        set_bit(STOP_SYNC_TIMER, &mdev->flags);
         }
 
         if (os.conn == C_CONNECTED &&
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 4249117f1f67..885471ded2fb 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -3803,7 +3803,6 @@ static void drbd_disconnect(struct drbd_conf *mdev)
 
         /* make sure syncer is stopped and w_resume_next_sg queued */
         del_timer_sync(&mdev->resync_timer);
-        set_bit(STOP_SYNC_TIMER, &mdev->flags);
         resync_timer_fn((unsigned long)mdev);
 
         /* wait for all w_e_end_data_req, w_e_end_rsdata_req, w_send_barrier,
diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 8be983263374..0e5bf8c98293 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -395,25 +395,22 @@ defer:
 
 void resync_timer_fn(unsigned long data)
 {
-        unsigned long flags;
         struct drbd_conf *mdev = (struct drbd_conf *) data;
         int queue;
 
-        spin_lock_irqsave(&mdev->req_lock, flags);
-
-        if (likely(!test_and_clear_bit(STOP_SYNC_TIMER, &mdev->flags))) {
-                queue = 1;
-                if (mdev->state.conn == C_VERIFY_S)
-                        mdev->resync_work.cb = w_make_ov_request;
-                else
-                        mdev->resync_work.cb = w_make_resync_request;
-        } else {
+        queue = 1;
+        switch (mdev->state.conn) {
+        case C_VERIFY_S:
+                mdev->resync_work.cb = w_make_ov_request;
+                break;
+        case C_SYNC_TARGET:
+                mdev->resync_work.cb = w_make_resync_request;
+                break;
+        default:
                 queue = 0;
                 mdev->resync_work.cb = w_resync_inactive;
         }
 
-        spin_unlock_irqrestore(&mdev->req_lock, flags);
-
         /* harmless race: list_empty outside data.work.q_lock */
         if (list_empty(&mdev->resync_work.list) && queue)
                 drbd_queue_work(&mdev->data.work, &mdev->resync_work);