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)
{
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);
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);
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,
atomic_inc(&isw_nr_in_flight);
- /*
- * Paired with synchronize_rcu() in cgroup_writeback_umount():
- * holding rcu_read_lock across inode_prepare_wbs_switch()
- * (covering the SB_ACTIVE check and the inode grab) and
- * wb_queue_isw() ensures synchronize_rcu() cannot return until
- * the work is queued, so the subsequent flush_workqueue() will
- * wait for the switch.
- */
- rcu_read_lock();
/* find and pin the new wb */
+ rcu_read_lock();
memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
if (memcg_css && !css_tryget(memcg_css))
memcg_css = NULL;
+ rcu_read_unlock();
if (!memcg_css)
goto out_free;
trace_inode_switch_wbs_queue(inode->i_wb, new_wb, 1);
wb_queue_isw(new_wb, isw);
- rcu_read_unlock();
return;
out_free:
- rcu_read_unlock();
atomic_dec(&isw_nr_in_flight);
if (new_wb)
wb_put(new_wb);
new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
nr = 0;
- /*
- * Paired with synchronize_rcu() in cgroup_writeback_umount().
- * Holding rcu_read_lock across the SB_ACTIVE check, the inode grab
- * and wb_queue_isw() ensures synchronize_rcu() cannot return until
- * the work is queued, so the subsequent flush_workqueue() will wait
- * for the switch.
- */
- rcu_read_lock();
spin_lock(&wb->list_lock);
/*
* In addition to the inodes that have completed writeback, also switch
/* no attached inodes? bail out */
if (nr == 0) {
- rcu_read_unlock();
atomic_dec(&isw_nr_in_flight);
wb_put(new_wb);
kfree(isw);
trace_inode_switch_wbs_queue(wb, new_wb, nr);
wb_queue_isw(new_wb, isw);
- rcu_read_unlock();
return restart;
}
}
/**
- * 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)) {
- /*
- * Paired with rcu_read_lock() in inode_switch_wbs() and
- * cleanup_offline_cgwb(). synchronize_rcu() waits for any
- * in-flight switcher that already passed the SB_ACTIVE check
- * to finish queueing its work, so flush_workqueue() below
- * will then drain it.
- */
- synchronize_rcu();
- flush_workqueue(isw_wq);
- }
+ cgroup_writeback_drain(sb);
}
static int __init cgroup_writeback_init(void)
projects / linux / commitdiff