With the previous three 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 unlocked_inode_to_wb transaction. This
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. There are three
exceptions.
* locked_inode_to_wb_and_lock_list() is holding wb->list_lock but the
wb may not be the inode's. Ensuring that is the function's role
after all. Updated to deref inode->i_wb directly.
* inode_wb_stat_unlocked_begin() is usually protected by combination
of !I_WB_SWITCH and rcu_read_lock(). Updated to deref inode->i_wb
directly.
* inode_congested() wants to test whether inode->i_wb is set before
starting the transaction. Added inode_to_wb_is_valid() which tests
inode->i_wb directly.
v5: might_lock() removed. It annotates that the lock is grabbed w/
irq enabled which isn't the case and triggering lockdep warning
spuriously.
v4: might_lock() added to unlocked_inode_to_wb_begin().
v3: inode_congested() conversion added.
v2: locked_inode_to_wb_and_lock_list() was missing in the first
version.
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>
---
fs/fs-writeback.c | 5 +++--
include/linux/backing-dev.h | 34 ++++++++++++++++++++++++++++++++--
2 files changed, 35 insertions(+), 4 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 25458fa..6b99dee 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -285,7 +285,8 @@ locked_inode_to_wb_and_lock_list(struct inode *inode)
spin_lock(&wb->list_lock);
wb_put(wb); /* not gonna deref it anymore */
- if (likely(wb == inode_to_wb(inode)))
+ /* i_wb may have changed inbetween, can't use inode_to_wb() */
+ if (likely(wb == inode->i_wb))
return wb; /* @inode already has ref */
spin_unlock(&wb->list_lock);
@@ -622,7 +623,7 @@ int inode_congested(struct inode *inode, int cong_bits)
* Once set, ->i_wb never becomes NULL while the inode is alive.
* Start transaction iff ->i_wb is visible.
*/
- if (inode && inode_to_wb(inode)) {
+ if (inode && inode_to_wb_is_valid(inode)) {
struct bdi_writeback *wb;
bool locked, congested;
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 73ffa32..dfce808 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -322,13 +322,33 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
}
/**
+ * inode_to_wb_is_valid - test whether an inode has a wb associated
+ * @inode: inode of interest
+ *
+ * Returns %true if @inode has a wb associated. May be called without any
+ * locking.
+ */
+static inline bool inode_to_wb_is_valid(struct inode *inode)
+{
+ return inode->i_wb;
+}
+
+/**
* 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 +380,12 @@ unlocked_inode_to_wb_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;
}
/**
@@ -459,6 +484,11 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
return &bdi->wb;
}
+static inline bool inode_to_wb_is_valid(struct inode *inode)
+{
+ return true;
+}
+
static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
{
return &inode_to_bdi(inode)->wb;
--
2.4.0
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