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 <[email protected]> --- 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
