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

Pull writeback fixes from Wu Fengguang:
 "Two writeback fixes

   - fix negative (setpoint - dirty) in 32bit archs

   - use down_read_trylock() in writeback_inodes_sb(_nr)_if_idle()"

* tag 'writeback-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux:
  Negative (setpoint-dirty) in bdi_position_ratio()
  vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

5 files changed, 29 insertions, 51 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 1e59ed575cc9..cf54bdfee334 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3689,20 +3689,6 @@ static int can_overcommit(struct btrfs_root *root,
         return 0;
 }
 
-static int writeback_inodes_sb_nr_if_idle_safe(struct super_block *sb,
-                                               unsigned long nr_pages,
-                                               enum wb_reason reason)
-{
-        if (!writeback_in_progress(sb->s_bdi) &&
-            down_read_trylock(&sb->s_umount)) {
-                writeback_inodes_sb_nr(sb, nr_pages, reason);
-                up_read(&sb->s_umount);
-                return 1;
-        }
-
-        return 0;
-}
-
 /*
  * shrink metadata reservation for delalloc
  */
@@ -3735,9 +3721,9 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
         while (delalloc_bytes && loops < 3) {
                 max_reclaim = min(delalloc_bytes, to_reclaim);
                 nr_pages = max_reclaim >> PAGE_CACHE_SHIFT;
-                writeback_inodes_sb_nr_if_idle_safe(root->fs_info->sb,
-                                                    nr_pages,
-                                                    WB_REASON_FS_FREE_SPACE);
+                try_to_writeback_inodes_sb_nr(root->fs_info->sb,
+                                              nr_pages,
+                                              WB_REASON_FS_FREE_SPACE);
 
                 /*
                  * We need to wait for the async pages to actually start before
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 9c4f4b1c97f8..9ea0cde3fa9e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2512,12 +2512,8 @@ static int ext4_nonda_switch(struct super_block *sb)
         /*
          * Start pushing delalloc when 1/2 of free blocks are dirty.
          */
-        if (dirty_blocks && (free_blocks < 2 * dirty_blocks) &&
-            !writeback_in_progress(sb->s_bdi) &&
-            down_read_trylock(&sb->s_umount)) {
-                writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
-                up_read(&sb->s_umount);
-        }
+        if (dirty_blocks && (free_blocks < 2 * dirty_blocks))
+                try_to_writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
 
         if (2 * free_blocks < 3 * dirty_blocks ||
                 free_blocks < (dirty_blocks + EXT4_FREECLUSTERS_WATERMARK)) {
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 359494ea1bde..21f46fb3a101 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1344,47 +1344,43 @@ void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
 EXPORT_SYMBOL(writeback_inodes_sb);
 
 /**
- * writeback_inodes_sb_if_idle  -       start writeback if none underway
+ * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
  * @sb: the superblock
- * @reason: reason why some writeback work was initiated
+ * @nr: the number of pages to write
+ * @reason: the reason of writeback
  *
- * Invoke writeback_inodes_sb if no writeback is currently underway.
+ * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
  */
-int writeback_inodes_sb_if_idle(struct super_block *sb, enum wb_reason reason)
+int try_to_writeback_inodes_sb_nr(struct super_block *sb,
+                                  unsigned long nr,
+                                  enum wb_reason reason)
 {
-        if (!writeback_in_progress(sb->s_bdi)) {
-                down_read(&sb->s_umount);
-                writeback_inodes_sb(sb, reason);
-                up_read(&sb->s_umount);
+        if (writeback_in_progress(sb->s_bdi))
                 return 1;
-        } else
+
+        if (!down_read_trylock(&sb->s_umount))
                 return 0;
+
+        writeback_inodes_sb_nr(sb, nr, reason);
+        up_read(&sb->s_umount);
+        return 1;
 }
-EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
+EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
 
 /**
- * writeback_inodes_sb_nr_if_idle       -       start writeback if none underway
+ * try_to_writeback_inodes_sb - try to start writeback if none underway
  * @sb: the superblock
- * @nr: the number of pages to write
  * @reason: reason why some writeback work was initiated
  *
- * Invoke writeback_inodes_sb if no writeback is currently underway.
+ * Implement by try_to_writeback_inodes_sb_nr()
  * Returns 1 if writeback was started, 0 if not.
  */
-int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
-                                   unsigned long nr,
-                                   enum wb_reason reason)
+int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
 {
-        if (!writeback_in_progress(sb->s_bdi)) {
-                down_read(&sb->s_umount);
-                writeback_inodes_sb_nr(sb, nr, reason);
-                up_read(&sb->s_umount);
-                return 1;
-        } else
-                return 0;
+        return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
 }
-EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
+EXPORT_SYMBOL(try_to_writeback_inodes_sb);
 
 /**
  * sync_inodes_sb       -       sync sb inode pages
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index b82a83aba311..9a9367c0c076 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -87,9 +87,9 @@ int inode_wait(void *);
 void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
 void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
                                                         enum wb_reason reason);
-int writeback_inodes_sb_if_idle(struct super_block *, enum wb_reason reason);
-int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr,
-                                                        enum wb_reason reason);
+int try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
+int try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
+                                  enum wb_reason reason);
 void sync_inodes_sb(struct super_block *);
 long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
                                 enum wb_reason reason);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 742c40583159..efe68148f621 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -696,7 +696,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
          *     => fast response on large errors; small oscillation near setpoint
          */
         setpoint = (freerun + limit) / 2;
-        x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
+        x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
                     limit - setpoint + 1);
         pos_ratio = x;
         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;