With the previous two patches, all operations which acquire wb from
inode are either under one of inode->i_lock, mapping->tree_lock or
wb->list_lock, or protected by stat transaction, which will be
depended upon by foreign inode wb switching.
This patch adds lockdep assertion to inode_to_wb() so that usages
outside the above list locks can be caught easily.
inode_wb_stat_unlocked_begin() is an exception as it's usually
protected by combination of !I_WB_SWITCH and rcu_read_lock(). It's
updated to dereference inode->i_wb directly.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
---
include/linux/backing-dev.h | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 040be1a..b9937e5 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -326,10 +326,18 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
* inode_to_wb - determine the wb of an inode
* @inode: inode of interest
*
- * Returns the wb @inode is currently associated with.
+ * Returns the wb @inode is currently associated with. The caller must be
+ * holding either @inode->i_lock, @inode->i_mapping->tree_lock, or the
+ * associated wb's list_lock.
*/
static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
{
+#ifdef CONFIG_LOCKDEP
+ WARN_ON_ONCE(debug_locks &&
+ (!lockdep_is_held(&inode->i_lock) &&
+ !lockdep_is_held(&inode->i_mapping->tree_lock) &&
+ !lockdep_is_held(&inode->i_wb->list_lock)));
+#endif
return inode->i_wb;
}
@@ -360,7 +368,12 @@ inode_wb_stat_unlocked_begin(struct inode *inode, bool *lockedp)
if (unlikely(*lockedp))
spin_lock_irq(&inode->i_mapping->tree_lock);
- return inode_to_wb(inode);
+
+ /*
+ * Protected by either !I_WB_SWITCH + rcu_read_lock() or tree_lock.
+ * inode_to_wb() will bark. Deref directly.
+ */
+ return inode->i_wb;
}
/**
--
2.1.0
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