writeback: add lockdep annotation to inode_to_wb()
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@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
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 @@
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 @@
* 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;