Currently switching of inode between different writeback structures is
asynchronous and not guaranteed to succeed. Add a variant of switching
that is synchronous and reliable so that it can reliably move inode to
the default writeback structure (bdi->wb) when writeback on bdi is going
to be shutdown.
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/fs-writeback.c | 60 ++++++++++++++++++++++++++++++++++++++++-------
include/linux/fs.h | 3 ++-
include/linux/writeback.h | 6 +++++
3 files changed, 60 insertions(+), 9 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 23dc97cf2a50..52992a1036b1 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -332,14 +332,11 @@ struct inode_switch_wbs_context {
struct work_struct work;
};
-static void inode_switch_wbs_work_fn(struct work_struct *work)
+static void do_inode_switch_wbs(struct inode *inode,
+ struct bdi_writeback *new_wb)
{
- struct inode_switch_wbs_context *isw =
- container_of(work, struct inode_switch_wbs_context, work);
- struct inode *inode = isw->inode;
struct address_space *mapping = inode->i_mapping;
struct bdi_writeback *old_wb = inode->i_wb;
- struct bdi_writeback *new_wb = isw->new_wb;
struct radix_tree_iter iter;
bool switched = false;
void **slot;
@@ -436,15 +433,29 @@ static void inode_switch_wbs_work_fn(struct work_struct *work)
spin_unlock(&new_wb->list_lock);
spin_unlock(&old_wb->list_lock);
+ /*
+ * Make sure waitqueue_active() check in wake_up_bit() cannot happen
+ * before I_WB_SWITCH is cleared. Pairs with the barrier in
+ * set_task_state() after wait_on_bit() added waiter to the wait queue.
+ */
+ smp_mb();
+ wake_up_bit(&inode->i_state, __I_WB_SWITCH);
+
if (switched) {
wb_wakeup(new_wb);
wb_put(old_wb);
}
- wb_put(new_wb);
+}
- iput(inode);
- kfree(isw);
+static void inode_switch_wbs_work_fn(struct work_struct *work)
+{
+ struct inode_switch_wbs_context *isw =
+ container_of(work, struct inode_switch_wbs_context, work);
+ do_inode_switch_wbs(isw->inode, isw->new_wb);
+ wb_put(isw->new_wb);
+ iput(isw->inode);
+ kfree(isw);
atomic_dec(&isw_nr_in_flight);
}
@@ -521,6 +532,39 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id)
}
/**
+ * inode_switch_to_default_wb_sync - change the wb association of an inode to
+ * the default writeback structure synchronously
+ * @inode: target inode
+ *
+ * Switch @inode's wb association to the default writeback structure (bdi->wb).
+ * Unlike inode_switch_wbs() the switching is performed synchronously and we
+ * guarantee the inode is switched to the default writeback structure when this
+ * function returns. Nothing prevents from someone else switching inode to
+ * another writeback structure just when we are done though. Preventing that is
+ * upto the caller if needed.
+ */
+void inode_switch_to_default_wb_sync(struct inode *inode)
+{
+ struct backing_dev_info *bdi = inode_to_bdi(inode);
+
+ /* while holding I_WB_SWITCH, no one else can update the association */
+ spin_lock(&inode->i_lock);
+ if (WARN_ON_ONCE(inode->i_state & I_FREEING) ||
+ !inode_to_wb_is_valid(inode) || inode_to_wb(inode) == &bdi->wb) {
+ spin_unlock(&inode->i_lock);
+ return;
+ }
+ __inode_wait_for_state_bit(inode, __I_WB_SWITCH);
+ inode->i_state |= I_WB_SWITCH;
+ spin_unlock(&inode->i_lock);
+
+ /* Make I_WB_SWITCH setting visible to unlocked users of i_wb */
+ synchronize_rcu();
+
+ do_inode_switch_wbs(inode, &bdi->wb);
+}
+
+/**
* wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
* @wbc: writeback_control of interest
* @inode: target inode
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c930cbc19342..319fb76f9081 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1929,7 +1929,8 @@ static inline bool HAS_UNMAPPED_ID(struct inode *inode)
#define I_DIRTY_TIME (1 << 11)
#define __I_DIRTY_TIME_EXPIRED 12
#define I_DIRTY_TIME_EXPIRED (1 << __I_DIRTY_TIME_EXPIRED)
-#define I_WB_SWITCH (1 << 13)
+#define __I_WB_SWITCH 13
+#define I_WB_SWITCH (1 << __I_WB_SWITCH)
#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)
#define I_DIRTY_ALL (I_DIRTY | I_DIRTY_TIME)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 5527d910ba3d..0d3ba83a0f7f 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -280,6 +280,8 @@ static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
bio_associate_blkcg(bio, wbc->wb->blkcg_css);
}
+void inode_switch_to_default_wb_sync(struct inode *inode);
+
#else /* CONFIG_CGROUP_WRITEBACK */
static inline void inode_attach_wb(struct inode *inode, struct page *page)
@@ -319,6 +321,10 @@ static inline void cgroup_writeback_umount(void)
{
}
+static inline void inode_switch_to_default_wb_sync(struct inode *inode)
+{
+}
+
#endif /* CONFIG_CGROUP_WRITEBACK */
/*
--
2.10.2
