#include <linux/wait.h> #include <linux/backing-dev.h> #include <linux/kthread.h> #include <linux/freezer.h> #include <linux/fs.h> #include <linux/pagemap.h> #include <linux/mm.h> #include <linux/sched.h> #include <linux/module.h> #include <linux/writeback.h> #include <linux/device.h> #include <trace/events/writeback.h> static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0); struct backing_dev_info default_backing_dev_info = { .name = "default", .ra_pages = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE, .state = 0, .capabilities = BDI_CAP_MAP_COPY, }; EXPORT_SYMBOL_GPL(default_backing_dev_info); struct backing_dev_info noop_backing_dev_info = { .name = "noop", .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK, }; EXPORT_SYMBOL_GPL(noop_backing_dev_info); static struct class *bdi_class; /* * bdi_lock protects updates to bdi_list and bdi_pending_list, as well as * reader side protection for bdi_pending_list. bdi_list has RCU reader side * locking. */ DEFINE_SPINLOCK(bdi_lock); LIST_HEAD(bdi_list); LIST_HEAD(bdi_pending_list); static struct task_struct *sync_supers_tsk; static struct timer_list sync_supers_timer; static int bdi_sync_supers(void *); static void sync_supers_timer_fn(unsigned long); void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2) { if (wb1 < wb2) { spin_lock(&wb1->list_lock); spin_lock_nested(&wb2->list_lock, 1); } else { spin_lock(&wb2->list_lock); spin_lock_nested(&wb1->list_lock, 1); } } #ifdef CONFIG_DEBUG_FS #include <linux/debugfs.h> #include <linux/seq_file.h> static struct dentry *bdi_debug_root; static void bdi_debug_init(void) { bdi_debug_root = debugfs_create_dir("bdi", NULL); } static int bdi_debug_stats_show(struct seq_file *m, void *v) { struct backing_dev_info *bdi = m->private; struct bdi_writeback *wb = &bdi->wb; unsigned long background_thresh; unsigned long dirty_thresh; unsigned long bdi_thresh; unsigned long nr_dirty, nr_io, nr_more_io; struct inode *inode; nr_dirty = nr_io = nr_more_io = 0; spin_lock(&wb->list_lock); list_for_each_entry(inode, &wb->b_dirty, i_wb_list) nr_dirty++; list_for_each_entry(inode, &wb->b_io, i_wb_list) nr_io++; list_for_each_entry(inode, &wb->b_more_io, i_wb_list) nr_more_io++; spin_unlock(&wb->list_lock); global_dirty_limits(&background_thresh, &dirty_thresh); bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); #define K(x) ((x) << (PAGE_SHIFT - 10)) seq_printf(m, "BdiWriteback: %10lu kB\n" "BdiReclaimable: %10lu kB\n" "BdiDirtyThresh: %10lu kB\n" "DirtyThresh: %10lu kB\n" "BackgroundThresh: %10lu kB\n" "BdiDirtied: %10lu kB\n" "BdiWritten: %10lu kB\n" "BdiWriteBandwidth: %10lu kBps\n" "b_dirty: %10lu\n" "b_io: %10lu\n" "b_more_io: %10lu\n" "bdi_list: %10u\n" "state: %10lx\n", (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)), (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)), K(bdi_thresh), K(dirty_thresh), K(background_thresh), (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)), (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)), (unsigned long) K(bdi->write_bandwidth), nr_dirty, nr_io, nr_more_io, !list_empty(&bdi->bdi_list), bdi->state); #undef K return 0; } static int bdi_debug_stats_open(struct inode *inode, struct file *file) { return single_open(file, bdi_debug_stats_show, inode->i_private); } static const struct file_operations bdi_debug_stats_fops = { .open = bdi_debug_stats_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, }; static void bdi_debug_register(struct backing_dev_info *bdi, const char *name) { bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root); bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir, bdi, &bdi_debug_stats_fops); } static void bdi_debug_unregister(struct backing_dev_info *bdi) { debugfs_remove(bdi->debug_stats); debugfs_remove(bdi->debug_dir); } #else static inline void bdi_debug_init(void) { } static inline void bdi_debug_register(struct backing_dev_info *bdi, const char *name) { } static inline void bdi_debug_unregister(struct backing_dev_info *bdi) { } #endif static ssize_t read_ahead_kb_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { struct backing_dev_info *bdi = dev_get_drvdata(dev); char *end; unsigned long read_ahead_kb; ssize_t ret = -EINVAL; read_ahead_kb = simple_strtoul(buf, &end, 10); if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) { bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10); ret = count; } return ret; } #define K(pages) ((pages) << (PAGE_SHIFT - 10)) #define BDI_SHOW(name, expr) \ static ssize_t name##_show(struct device *dev, \ struct device_attribute *attr, char *page) \ { \ struct backing_dev_info *bdi = dev_get_drvdata(dev); \ \ return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr); \ } BDI_SHOW(read_ahead_kb, K(bdi->ra_pages)) static ssize_t min_ratio_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { struct backing_dev_info *bdi = dev_get_drvdata(dev); char *end; unsigned int ratio; ssize_t ret = -EINVAL; ratio = simple_strtoul(buf, &end, 10); if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) { ret = bdi_set_min_ratio(bdi, ratio); if (!ret) ret = count; } return ret; } BDI_SHOW(min_ratio, bdi->min_ratio) static ssize_t max_ratio_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { struct backing_dev_info *bdi = dev_get_drvdata(dev); char *end; unsigned int ratio; ssize_t ret = -EINVAL; ratio = simple_strtoul(buf, &end, 10); if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) { ret = bdi_set_max_ratio(bdi, ratio); if (!ret) ret = count; } return ret; } BDI_SHOW(max_ratio, bdi->max_ratio) #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store) static struct device_attribute bdi_dev_attrs[] = { __ATTR_RW(read_ahead_kb), __ATTR_RW(min_ratio), __ATTR_RW(max_ratio), __ATTR_NULL, }; static __init int bdi_class_init(void) { bdi_class = class_create(THIS_MODULE, "bdi"); if (IS_ERR(bdi_class)) return PTR_ERR(bdi_class); bdi_class->dev_attrs = bdi_dev_attrs; bdi_debug_init(); return 0; } postcore_initcall(bdi_class_init); static int __init default_bdi_init(void) { int err; sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers"); BUG_ON(IS_ERR(sync_supers_tsk)); setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0); bdi_arm_supers_timer(); err = bdi_init(&default_backing_dev_info); if (!err) bdi_register(&default_backing_dev_info, NULL, "default"); err = bdi_init(&noop_backing_dev_info); return err; } subsys_initcall(default_bdi_init); int bdi_has_dirty_io(struct backing_dev_info *bdi) { return wb_has_dirty_io(&bdi->wb); } /* * kupdated() used to do this. We cannot do it from the bdi_forker_thread() * or we risk deadlocking on ->s_umount. The longer term solution would be * to implement sync_supers_bdi() or similar and simply do it from the * bdi writeback thread individually. */ static int bdi_sync_supers(void *unused) { set_user_nice(current, 0); while (!kthread_should_stop()) { set_current_state(TASK_INTERRUPTIBLE); schedule(); /* * Do this periodically, like kupdated() did before. */ sync_supers(); } return 0; } void bdi_arm_supers_timer(void) { unsigned long next; if (!dirty_writeback_interval) return; next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies; mod_timer(&sync_supers_timer, round_jiffies_up(next)); } static void sync_supers_timer_fn(unsigned long unused) { wake_up_process(sync_supers_tsk); bdi_arm_supers_timer(); } static void wakeup_timer_fn(unsigned long data) { struct backing_dev_info *bdi = (struct backing_dev_info *)data; spin_lock_bh(&bdi->wb_lock); if (bdi->wb.task) { trace_writeback_wake_thread(bdi); wake_up_process(bdi->wb.task); } else { /* * When bdi tasks are inactive for long time, they are killed. * In this case we have to wake-up the forker thread which * should create and run the bdi thread. */ trace_writeback_wake_forker_thread(bdi); wake_up_process(default_backing_dev_info.wb.task); } spin_unlock_bh(&bdi->wb_lock); } /* * This function is used when the first inode for this bdi is marked dirty. It * wakes-up the corresponding bdi thread which should then take care of the * periodic background write-out of dirty inodes. Since the write-out would * starts only 'dirty_writeback_interval' centisecs from now anyway, we just * set up a timer which wakes the bdi thread up later. * * Note, we wouldn't bother setting up the timer, but this function is on the * fast-path (used by '__mark_inode_dirty()'), so we save few context switches * by delaying the wake-up. */ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi) { unsigned long timeout; timeout = msecs_to_jiffies(dirty_writeback_interval * 10); mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout); } /* * Calculate the longest interval (jiffies) bdi threads are allowed to be * inactive. */ static unsigned long bdi_longest_inactive(void) { unsigned long interval; interval = msecs_to_jiffies(dirty_writeback_interval * 10); return max(5UL * 60 * HZ, interval); } /* * Clear pending bit and wakeup anybody waiting for flusher thread creation or * shutdown */ static void bdi_clear_pending(struct backing_dev_info *bdi) { clear_bit(BDI_pending, &bdi->state); smp_mb__after_clear_bit(); wake_up_bit(&bdi->state, BDI_pending); } static int bdi_forker_thread(void *ptr) { struct bdi_writeback *me = ptr; current->flags |= PF_SWAPWRITE; set_freezable(); /* * Our parent may run at a different priority, just set us to normal */ set_user_nice(current, 0); for (;;) { struct task_struct *task = NULL; struct backing_dev_info *bdi; enum { NO_ACTION, /* Nothing to do */ FORK_THREAD, /* Fork bdi thread */ KILL_THREAD, /* Kill inactive bdi thread */ } action = NO_ACTION; /* * Temporary measure, we want to make sure we don't see * dirty data on the default backing_dev_info */ if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) { del_timer(&me->wakeup_timer); wb_do_writeback(me, 0); } spin_lock_bh(&bdi_lock); /* * In the following loop we are going to check whether we have * some work to do without any synchronization with tasks * waking us up to do work for them. Set the task state here * so that we don't miss wakeups after verifying conditions. */ set_current_state(TASK_INTERRUPTIBLE); list_for_each_entry(bdi, &bdi_list, bdi_list) { bool have_dirty_io; if (!bdi_cap_writeback_dirty(bdi) || bdi_cap_flush_forker(bdi)) continue; WARN(!test_bit(BDI_registered, &bdi->state), "bdi %p/%s is not registered!\n", bdi, bdi->name); have_dirty_io = !list_empty(&bdi->work_list) || wb_has_dirty_io(&bdi->wb); /* * If the bdi has work to do, but the thread does not * exist - create it. */ if (!bdi->wb.task && have_dirty_io) { /* * Set the pending bit - if someone will try to * unregister this bdi - it'll wait on this bit. */ set_bit(BDI_pending, &bdi->state); action = FORK_THREAD; break; } spin_lock(&bdi->wb_lock); /* * If there is no work to do and the bdi thread was * inactive long enough - kill it. The wb_lock is taken * to make sure no-one adds more work to this bdi and * wakes the bdi thread up. */ if (bdi->wb.task && !have_dirty_io && time_after(jiffies, bdi->wb.last_active + bdi_longest_inactive())) { task = bdi->wb.task; bdi->wb.task = NULL; spin_unlock(&bdi->wb_lock); set_bit(BDI_pending, &bdi->state); action = KILL_THREAD; break; } spin_unlock(&bdi->wb_lock); } spin_unlock_bh(&bdi_lock); /* Keep working if default bdi still has things to do */ if (!list_empty(&me->bdi->work_list)) __set_current_state(TASK_RUNNING); switch (action) { case FORK_THREAD: __set_current_state(TASK_RUNNING); task = kthread_create(bdi_writeback_thread, &bdi->wb, "flush-%s", dev_name(bdi->dev)); if (IS_ERR(task)) { /* * If thread creation fails, force writeout of * the bdi from the thread. Hopefully 1024 is * large enough for efficient IO. */ writeback_inodes_wb(&bdi->wb, 1024, WB_REASON_FORKER_THREAD); } else { /* * The spinlock makes sure we do not lose * wake-ups when racing with 'bdi_queue_work()'. * And as soon as the bdi thread is visible, we * can start it. */ spin_lock_bh(&bdi->wb_lock); bdi->wb.task = task; spin_unlock_bh(&bdi->wb_lock); wake_up_process(task); } bdi_clear_pending(bdi); break; case KILL_THREAD: __set_current_state(TASK_RUNNING); kthread_stop(task); bdi_clear_pending(bdi); break; case NO_ACTION: if (!wb_has_dirty_io(me) || !dirty_writeback_interval) /* * There are no dirty data. The only thing we * should now care about is checking for * inactive bdi threads and killing them. Thus, * let's sleep for longer time, save energy and * be friendly for battery-driven devices. */ schedule_timeout(bdi_longest_inactive()); else schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10)); try_to_freeze(); break; } } return 0; } /* * Remove bdi from bdi_list, and ensure that it is no longer visible */ static void bdi_remove_from_list(struct backing_dev_info *bdi) { spin_lock_bh(&bdi_lock); list_del_rcu(&bdi->bdi_list); spin_unlock_bh(&bdi_lock); synchronize_rcu_expedited(); } int bdi_register(struct backing_dev_info *bdi, struct device *parent, const char *fmt, ...) { va_list args; struct device *dev; if (bdi->dev) /* The driver needs to use separate queues per device */ return 0; va_start(args, fmt); dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args); va_end(args); if (IS_ERR(dev)) return PTR_ERR(dev); bdi->dev = dev; /* * Just start the forker thread for our default backing_dev_info, * and add other bdi's to the list. They will get a thread created * on-demand when they need it. */ if (bdi_cap_flush_forker(bdi)) { struct bdi_writeback *wb = &bdi->wb; wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s", dev_name(dev)); if (IS_ERR(wb->task)) return PTR_ERR(wb->task); } bdi_debug_register(bdi, dev_name(dev)); set_bit(BDI_registered, &bdi->state); spin_lock_bh(&bdi_lock); list_add_tail_rcu(&bdi->bdi_list, &bdi_list); spin_unlock_bh(&bdi_lock); trace_writeback_bdi_register(bdi); return 0; } EXPORT_SYMBOL(bdi_register); int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev) { return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev)); } EXPORT_SYMBOL(bdi_register_dev); /* * Remove bdi from the global list and shutdown any threads we have running */ static void bdi_wb_shutdown(struct backing_dev_info *bdi) { if (!bdi_cap_writeback_dirty(bdi)) return; /* * Make sure nobody finds us on the bdi_list anymore */ bdi_remove_from_list(bdi); /* * If setup is pending, wait for that to complete first */ wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait, TASK_UNINTERRUPTIBLE); /* * Finally, kill the kernel thread. We don't need to be RCU * safe anymore, since the bdi is gone from visibility. Force * unfreeze of the thread before calling kthread_stop(), otherwise * it would never exet if it is currently stuck in the refrigerator. */ if (bdi->wb.task) { thaw_process(bdi->wb.task); kthread_stop(bdi->wb.task); } } /* * This bdi is going away now, make sure that no super_blocks point to it */ static void bdi_prune_sb(struct backing_dev_info *bdi) { struct super_block *sb; spin_lock(&sb_lock); list_for_each_entry(sb, &super_blocks, s_list) { if (sb->s_bdi == bdi) sb->s_bdi = &default_backing_dev_info; } spin_unlock(&sb_lock); } void bdi_unregister(struct backing_dev_info *bdi) { if (bdi->dev) { bdi_set_min_ratio(bdi, 0); trace_writeback_bdi_unregister(bdi); bdi_prune_sb(bdi); del_timer_sync(&bdi->wb.wakeup_timer); if (!bdi_cap_flush_forker(bdi)) bdi_wb_shutdown(bdi); bdi_debug_unregister(bdi); device_unregister(bdi->dev); bdi->dev = NULL; } } EXPORT_SYMBOL(bdi_unregister); static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi) { memset(wb, 0, sizeof(*wb)); wb->bdi = bdi; wb->last_old_flush = jiffies; INIT_LIST_HEAD(&wb->b_dirty); INIT_LIST_HEAD(&wb->b_io); INIT_LIST_HEAD(&wb->b_more_io); spin_lock_init(&wb->list_lock); setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi); } /* * Initial write bandwidth: 100 MB/s */ #define INIT_BW (100 << (20 - PAGE_SHIFT)) int bdi_init(struct backing_dev_info *bdi) { int i, err; bdi->dev = NULL; bdi->min_ratio = 0; bdi->max_ratio = 100; bdi->max_prop_frac = PROP_FRAC_BASE; spin_lock_init(&bdi->wb_lock); INIT_LIST_HEAD(&bdi->bdi_list); INIT_LIST_HEAD(&bdi->work_list); bdi_wb_init(&bdi->wb, bdi); for (i = 0; i < NR_BDI_STAT_ITEMS; i++) { err = percpu_counter_init(&bdi->bdi_stat[i], 0); if (err) goto err; } bdi->dirty_exceeded = 0; bdi->bw_time_stamp = jiffies; bdi->written_stamp = 0; bdi->balanced_dirty_ratelimit = INIT_BW; bdi->dirty_ratelimit = INIT_BW; bdi->write_bandwidth = INIT_BW; bdi->avg_write_bandwidth = INIT_BW; err = prop_local_init_percpu(&bdi->completions); if (err) { err: while (i--) percpu_counter_destroy(&bdi->bdi_stat[i]); } return err; } EXPORT_SYMBOL(bdi_init); void bdi_destroy(struct backing_dev_info *bdi) { int i; /* * Splice our entries to the default_backing_dev_info, if this * bdi disappears */ if (bdi_has_dirty_io(bdi)) { struct bdi_writeback *dst = &default_backing_dev_info.wb; bdi_lock_two(&bdi->wb, dst); list_splice(&bdi->wb.b_dirty, &dst->b_dirty); list_splice(&bdi->wb.b_io, &dst->b_io); list_splice(&bdi->wb.b_more_io, &dst->b_more_io); spin_unlock(&bdi->wb.list_lock); spin_unlock(&dst->list_lock); } bdi_unregister(bdi); /* * If bdi_unregister() had already been called earlier, the * wakeup_timer could still be armed because bdi_prune_sb() * can race with the bdi_wakeup_thread_delayed() calls from * __mark_inode_dirty(). */ del_timer_sync(&bdi->wb.wakeup_timer); for (i = 0; i < NR_BDI_STAT_ITEMS; i++) percpu_counter_destroy(&bdi->bdi_stat[i]); prop_local_destroy_percpu(&bdi->completions); } EXPORT_SYMBOL(bdi_destroy); /* * For use from filesystems to quickly init and register a bdi associated * with dirty writeback */ int bdi_setup_and_register(struct backing_dev_info *bdi, char *name, unsigned int cap) { char tmp[32]; int err; bdi->name = name; bdi->capabilities = cap; err = bdi_init(bdi); if (err) return err; sprintf(tmp, "%.28s%s", name, "-%d"); err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq)); if (err) { bdi_destroy(bdi); return err; } return 0; } EXPORT_SYMBOL(bdi_setup_and_register); static wait_queue_head_t congestion_wqh[2] = { __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]), __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1]) }; static atomic_t nr_bdi_congested[2]; void clear_bdi_congested(struct backing_dev_info *bdi, int sync) { enum bdi_state bit; wait_queue_head_t *wqh = &congestion_wqh[sync]; bit = sync ? BDI_sync_congested : BDI_async_congested; if (test_and_clear_bit(bit, &bdi->state)) atomic_dec(&nr_bdi_congested[sync]); smp_mb__after_clear_bit(); if (waitqueue_active(wqh)) wake_up(wqh); } EXPORT_SYMBOL(clear_bdi_congested); void set_bdi_congested(struct backing_dev_info *bdi, int sync) { enum bdi_state bit; bit = sync ? BDI_sync_congested : BDI_async_congested; if (!test_and_set_bit(bit, &bdi->state)) atomic_inc(&nr_bdi_congested[sync]); } EXPORT_SYMBOL(set_bdi_congested); /** * congestion_wait - wait for a backing_dev to become uncongested * @sync: SYNC or ASYNC IO * @timeout: timeout in jiffies * * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit * write congestion. If no backing_devs are congested then just wait for the * next write to be completed. */ long congestion_wait(int sync, long timeout) { long ret; unsigned long start = jiffies; DEFINE_WAIT(wait); wait_queue_head_t *wqh = &congestion_wqh[sync]; prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); ret = io_schedule_timeout(timeout); finish_wait(wqh, &wait); trace_writeback_congestion_wait(jiffies_to_usecs(timeout), jiffies_to_usecs(jiffies - start)); return ret; } EXPORT_SYMBOL(congestion_wait); /** * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes * @zone: A zone to check if it is heavily congested * @sync: SYNC or ASYNC IO * @timeout: timeout in jiffies * * In the event of a congested backing_dev (any backing_dev) and the given * @zone has experienced recent congestion, this waits for up to @timeout * jiffies for either a BDI to exit congestion of the given @sync queue * or a write to complete. * * In the absence of zone congestion, cond_resched() is called to yield * the processor if necessary but otherwise does not sleep. * * The return value is 0 if the sleep is for the full timeout. Otherwise, * it is the number of jiffies that were still remaining when the function * returned. return_value == timeout implies the function did not sleep. */ long wait_iff_congested(struct zone *zone, int sync, long timeout) { long ret; unsigned long start = jiffies; DEFINE_WAIT(wait); wait_queue_head_t *wqh = &congestion_wqh[sync]; /* * If there is no congestion, or heavy congestion is not being * encountered in the current zone, yield if necessary instead * of sleeping on the congestion queue */ if (atomic_read(&nr_bdi_congested[sync]) == 0 || !zone_is_reclaim_congested(zone)) { cond_resched(); /* In case we scheduled, work out time remaining */ ret = timeout - (jiffies - start); if (ret < 0) ret = 0; goto out; } /* Sleep until uncongested or a write happens */ prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); ret = io_schedule_timeout(timeout); finish_wait(wqh, &wait); out: trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout), jiffies_to_usecs(jiffies - start)); return ret; } EXPORT_SYMBOL(wait_iff_congested);