Hi Jens, I've noticed the following _possible_ issue.
Jens Axboe wrote:
+static int bdi_forker_task(void *ptr)
+{
+ struct backing_dev_info *me = ptr;
+
+ for (;;) {
+ struct backing_dev_info *bdi, *tmp;
+
+ /*
+ * Temporary measure, we want to make sure we don't see
+ * dirty data on the default backing_dev_info
+ */
+ if (bdi_has_dirty_io(me))
+ bdi_flush_io(me);
+
+ spin_lock(&bdi_lock);
+
+ /*
+ * Check if any existing bdi's have dirty data without
+ * a thread registered. If so, set that up.
+ */
+ list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
+ if (bdi->task || !bdi_has_dirty_io(bdi))
+ continue;
+
+ bdi_add_default_flusher_task(bdi);
+ }
+
+ set_current_state(TASK_INTERRUPTIBLE);
+
What happens if we are preempted here? Since we have TASK_INTERRUPTIBLE
state, we will not come back unless some other task wakes us up. Who
would wake us up in this case?
+ if (list_empty(&bdi_pending_list)) {
+ unsigned long wait;
+
+ spin_unlock(&bdi_lock);
+ wait = msecs_to_jiffies(dirty_writeback_interval * 10);
+ schedule_timeout(wait);
+ try_to_freeze();
+ continue;
+ }
+
+ __set_current_state(TASK_RUNNING);
+
+ /*
+ * This is our real job - check for pending entries in
+ * bdi_pending_list, and create the tasks that got added
+ */
+ bdi = list_entry(bdi_pending_list.next, struct backing_dev_info,
+ bdi_list);
+ list_del_init(&bdi->bdi_list);
+ spin_unlock(&bdi_lock);
+
+ BUG_ON(bdi->task);
+
+ bdi->task = kthread_run(bdi_start_fn, bdi, "flush-%s",
+ dev_name(bdi->dev));
+ /*
+ * If task creation fails, then readd the bdi to
+ * the pending list and force writeout of the bdi
+ * from this forker thread. That will free some memory
+ * and we can try again.
+ */
+ if (IS_ERR(bdi->task)) {
+ bdi->task = NULL;
+
+ /*
+ * Add this 'bdi' to the back, so we get
+ * a chance to flush other bdi's to free
+ * memory.
+ */
+ spin_lock(&bdi_lock);
+ list_add_tail(&bdi->bdi_list, &bdi_pending_list);
+ spin_unlock(&bdi_lock);
+
+ bdi_flush_io(bdi);
+ }
+ }
+
+ return 0;
+}
--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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