Merge tag 'writeback-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux

fix 1 mysterious divide error
fix 3 NULL dereference bugs in writeback tracing, on SD card removal w/o umount

* tag 'writeback-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux:
  writeback: fix dereferencing NULL bdi->dev on trace_writeback_queue
  lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel
  writeback: fix NULL bdi->dev in trace writeback_single_inode
  backing-dev: fix wakeup timer races with bdi_unregister()

4 files changed, 35 insertions, 15 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index f855916657ba..5b4a9362d5aa 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -53,14 +53,6 @@ struct wb_writeback_work {
 };
 
 /*
- * Include the creation of the trace points after defining the
- * wb_writeback_work structure so that the definition remains local to this
- * file.
- */
-#define CREATE_TRACE_POINTS
-#include <trace/events/writeback.h>
-
-/*
  * We don't actually have pdflush, but this one is exported though /proc...
  */
 int nr_pdflush_threads;
@@ -92,6 +84,14 @@ static inline struct inode *wb_inode(struct list_head *head)
         return list_entry(head, struct inode, i_wb_list);
 }
 
+/*
+ * Include the creation of the trace points after defining the
+ * wb_writeback_work structure and inline functions so that the definition
+ * remains local to this file.
+ */
+#define CREATE_TRACE_POINTS
+#include <trace/events/writeback.h>
+
 /* Wakeup flusher thread or forker thread to fork it. Requires bdi->wb_lock. */
 static void bdi_wakeup_flusher(struct backing_dev_info *bdi)
 {
diff --git a/include/linux/proportions.h b/include/linux/proportions.h
index ef35bb73f69b..26a8a4ed9b07 100644
--- a/include/linux/proportions.h
+++ b/include/linux/proportions.h
@@ -81,7 +81,11 @@ void prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
  * Limit the time part in order to ensure there are some bits left for the
  * cycle counter and fraction multiply.
  */
+#if BITS_PER_LONG == 32
 #define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
+#else
+#define PROP_MAX_SHIFT (BITS_PER_LONG/2)
+#endif
 
 #define PROP_FRAC_SHIFT         (BITS_PER_LONG - PROP_MAX_SHIFT - 1)
 #define PROP_FRAC_BASE          (1UL << PROP_FRAC_SHIFT)
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 8588a8918023..5973410e8f8c 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -47,7 +47,10 @@ DECLARE_EVENT_CLASS(writeback_work_class,
                 __field(int, reason)
         ),
         TP_fast_assign(
-                strncpy(__entry->name, dev_name(bdi->dev), 32);
+                struct device *dev = bdi->dev;
+                if (!dev)
+                        dev = default_backing_dev_info.dev;
+                strncpy(__entry->name, dev_name(dev), 32);
                 __entry->nr_pages = work->nr_pages;
                 __entry->sb_dev = work->sb ? work->sb->s_dev : 0;
                 __entry->sync_mode = work->sync_mode;
@@ -426,7 +429,7 @@ DECLARE_EVENT_CLASS(writeback_single_inode_template,
 
         TP_fast_assign(
                 strncpy(__entry->name,
-                        dev_name(inode->i_mapping->backing_dev_info->dev), 32);
+                        dev_name(inode_to_bdi(inode)->dev), 32);
                 __entry->ino            = inode->i_ino;
                 __entry->state          = inode->i_state;
                 __entry->dirtied_when   = inode->dirtied_when;
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7ba8feae11b8..dd8e2aafb07e 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -318,7 +318,7 @@ static void wakeup_timer_fn(unsigned long data)
         if (bdi->wb.task) {
                 trace_writeback_wake_thread(bdi);
                 wake_up_process(bdi->wb.task);
-        } else {
+        } else if (bdi->dev) {
                 /*
                  * When bdi tasks are inactive for long time, they are killed.
                  * In this case we have to wake-up the forker thread which
@@ -584,6 +584,8 @@ EXPORT_SYMBOL(bdi_register_dev);
  */
 static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 {
+        struct task_struct *task;
+
         if (!bdi_cap_writeback_dirty(bdi))
                 return;
 
@@ -602,8 +604,13 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
          * Finally, kill the kernel thread. We don't need to be RCU
          * safe anymore, since the bdi is gone from visibility.
          */
-        if (bdi->wb.task)
-                kthread_stop(bdi->wb.task);
+        spin_lock_bh(&bdi->wb_lock);
+        task = bdi->wb.task;
+        bdi->wb.task = NULL;
+        spin_unlock_bh(&bdi->wb_lock);
+
+        if (task)
+                kthread_stop(task);
 }
 
 /*
@@ -623,7 +630,9 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
 
 void bdi_unregister(struct backing_dev_info *bdi)
 {
-        if (bdi->dev) {
+        struct device *dev = bdi->dev;
+
+        if (dev) {
                 bdi_set_min_ratio(bdi, 0);
                 trace_writeback_bdi_unregister(bdi);
                 bdi_prune_sb(bdi);
@@ -632,8 +641,12 @@ void bdi_unregister(struct backing_dev_info *bdi)
                 if (!bdi_cap_flush_forker(bdi))
                         bdi_wb_shutdown(bdi);
                 bdi_debug_unregister(bdi);
-                device_unregister(bdi->dev);
+
+                spin_lock_bh(&bdi->wb_lock);
                 bdi->dev = NULL;
+                spin_unlock_bh(&bdi->wb_lock);
+
+                device_unregister(dev);
         }
 }
 EXPORT_SYMBOL(bdi_unregister);