diff options
| -rw-r--r-- | fs/fs-writeback.c | 71 | ||||
| -rw-r--r-- | include/linux/fs/super_types.h | 8 |
2 files changed, 53 insertions, 26 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index a65694cbfe68..900ad7818bd4 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -497,6 +497,23 @@ skip_switch: return switched; } +static inline void cgroup_writeback_pin(struct super_block *sb) +{ + atomic_inc(&sb->s_isw_nr_in_flight); +} + +static inline void cgroup_writeback_unpin(struct super_block *sb) +{ + if (atomic_dec_and_test(&sb->s_isw_nr_in_flight)) + wake_up_var(&sb->s_isw_nr_in_flight); +} + +static inline void cgroup_writeback_drain(struct super_block *sb) +{ + wait_var_event(&sb->s_isw_nr_in_flight, + !atomic_read(&sb->s_isw_nr_in_flight)); +} + static void process_inode_switch_wbs(struct bdi_writeback *new_wb, struct inode_switch_wbs_context *isw) { @@ -554,8 +571,12 @@ relock: wb_put_many(old_wb, nr_switched); } - for (inodep = isw->inodes; *inodep; inodep++) + for (inodep = isw->inodes; *inodep; inodep++) { + struct super_block *sb = (*inodep)->i_sb; + iput(*inodep); + cgroup_writeback_unpin(sb); + } wb_put(new_wb); kfree(isw); atomic_dec(&isw_nr_in_flight); @@ -598,16 +619,19 @@ void inode_switch_wbs_work_fn(struct work_struct *work) static bool inode_prepare_wbs_switch(struct inode *inode, struct bdi_writeback *new_wb) { + /* Avoid the atomic_inc/smp_mb dance once SB_ACTIVE is gone. */ + if (!(inode->i_sb->s_flags & SB_ACTIVE)) + return false; + /* - * Paired with smp_mb() in cgroup_writeback_umount(). - * isw_nr_in_flight must be increased before checking SB_ACTIVE and - * grabbing an inode, otherwise isw_nr_in_flight can be observed as 0 - * in cgroup_writeback_umount() and the isw_wq will be not flushed. + * Pairs with smp_mb() in cgroup_writeback_umount(): the umounter either + * sees a non-zero counter and waits, or we see SB_ACTIVE clear below. */ + cgroup_writeback_pin(inode->i_sb); smp_mb(); if (IS_DAX(inode)) - return false; + goto out_unpin; /* while holding I_WB_SWITCH, no one else can update the association */ spin_lock(&inode->i_lock); @@ -615,13 +639,17 @@ static bool inode_prepare_wbs_switch(struct inode *inode, inode_state_read(inode) & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) || inode_to_wb(inode) == new_wb) { spin_unlock(&inode->i_lock); - return false; + goto out_unpin; } inode_state_set(inode, I_WB_SWITCH); __iget(inode); spin_unlock(&inode->i_lock); return true; + +out_unpin: + cgroup_writeback_unpin(inode->i_sb); + return false; } static void wb_queue_isw(struct bdi_writeback *wb, @@ -1198,36 +1226,27 @@ out_bdi_put: } /** - * cgroup_writeback_umount - flush inode wb switches for umount + * cgroup_writeback_umount - wait for in-flight inode wb switches on @sb * @sb: target super_block * - * This function is called when a super_block is about to be destroyed and - * flushes in-flight inode wb switches. An inode wb switch goes through - * RCU and then workqueue, so the two need to be flushed in order to ensure - * that all previously scheduled switches are finished. As wb switches are - * rare occurrences and synchronize_rcu() can take a while, perform - * flushing iff wb switches are in flight. + * Wait until every inode wb switch that already passed the SB_ACTIVE + * check on this superblock has been completed by the worker. Since + * SB_ACTIVE is cleared before this is called, no new switches can start + * for @sb, so s_isw_nr_in_flight will monotonically drop to zero. */ void cgroup_writeback_umount(struct super_block *sb) { - if (!(sb->s_bdi->capabilities & BDI_CAP_WRITEBACK)) return; /* - * SB_ACTIVE should be reliably cleared before checking - * isw_nr_in_flight, see generic_shutdown_super(). + * Pairs with smp_mb() in inode_prepare_wbs_switch(): we either observe + * a non-zero counter and wait, or the switcher sees SB_ACTIVE clear + * (cleared by generic_shutdown_super()) and bails before grabbing the + * inode. */ smp_mb(); - - if (atomic_read(&isw_nr_in_flight)) { - /* - * Use rcu_barrier() to wait for all pending callbacks to - * ensure that all in-flight wb switches are in the workqueue. - */ - rcu_barrier(); - flush_workqueue(isw_wq); - } + cgroup_writeback_drain(sb); } static int __init cgroup_writeback_init(void) diff --git a/include/linux/fs/super_types.h b/include/linux/fs/super_types.h index 383050e7fdf5..1ab4e2265129 100644 --- a/include/linux/fs/super_types.h +++ b/include/linux/fs/super_types.h @@ -274,6 +274,14 @@ struct super_block { /* number of fserrors that are being sent to fsnotify/filesystems */ refcount_t s_pending_errors; + +#ifdef CONFIG_CGROUP_WRITEBACK + /* + * Number of in-flight inode wb switches for this sb. Drained by + * cgroup_writeback_umount() before tear-down. + */ + atomic_t s_isw_nr_in_flight; +#endif } __randomize_layout; /* |