writeback: check for registered bdi in flusher add and inode dirty

Also a debugging aid. We want to catch dirty inodes being added to
backing devices that don't do writeback.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 16 insertions, 0 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 2e601ce581c9..da86ef58e427 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1046,6 +1046,14 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                  */
                 if (!was_dirty) {
                         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
+                        struct backing_dev_info *bdi = wb->bdi;
+
+                        if (bdi_cap_writeback_dirty(bdi) &&
+                            !test_bit(BDI_registered, &bdi->state)) {
+                                WARN_ON(1);
+                                printk(KERN_ERR "bdi-%s not registered\n",
+                                                                bdi->name);
+                        }
 
                         inode->dirtied_when = jiffies;
                         list_move(&inode->i_list, &wb->b_dirty);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 2f218b7cb063..f169bcb90b58 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -29,6 +29,7 @@ enum bdi_state {
         BDI_wb_alloc,           /* Default embedded wb allocated */
         BDI_async_congested,    /* The async (write) queue is getting full */
         BDI_sync_congested,     /* The sync queue is getting full */
+        BDI_registered,         /* bdi_register() was done */
         BDI_unused,             /* Available bits start here */
 };
 
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 5cb32c5b93d8..d3ca0dac1111 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -465,6 +465,12 @@ void static bdi_add_default_flusher_task(struct backing_dev_info *bdi)
         if (!bdi_cap_writeback_dirty(bdi))
                 return;
 
+        if (WARN_ON(!test_bit(BDI_registered, &bdi->state))) {
+                printk(KERN_ERR "bdi %p/%s is not registered!\n",
+                                                        bdi, bdi->name);
+                return;
+        }
+
         /*
          * Check with the helper whether to proceed adding a task. Will only
          * abort if we two or more simultanous calls to
@@ -528,6 +534,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
         }
 
         bdi_debug_register(bdi, dev_name(dev));
+        set_bit(BDI_registered, &bdi->state);
 exit:
         return ret;
 }