3 files changed, 72 insertions, 197 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8cc06d5432b5..d5be1693ac93 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -38,43 +38,18 @@ int nr_pdflush_threads;
 /*
  * Passed into wb_writeback(), essentially a subset of writeback_control
  */
-struct wb_writeback_args {
+struct wb_writeback_work {
         long nr_pages;
         struct super_block *sb;
         enum writeback_sync_modes sync_mode;
         unsigned int for_kupdate:1;
         unsigned int range_cyclic:1;
         unsigned int for_background:1;
-};
 
-/*
- * Work items for the bdi_writeback threads
- */
-struct bdi_work {
         struct list_head list;          /* pending work list */
-        struct rcu_head rcu_head;       /* for RCU free/clear of work */
-
-        unsigned long seen;             /* threads that have seen this work */
-        atomic_t pending;               /* number of threads still to do work */
-
-        struct wb_writeback_args args;  /* writeback arguments */
-
-        unsigned long state;            /* flag bits, see WS_* */
-};
-
-enum {
-        WS_INPROGRESS = 0,
-        WS_ONSTACK,
+        struct completion *done;        /* set if the caller waits */
 };
 
-static inline void bdi_work_init(struct bdi_work *work,
-                                 struct wb_writeback_args *args)
-{
-        INIT_RCU_HEAD(&work->rcu_head);
-        work->args = *args;
-        __set_bit(WS_INPROGRESS, &work->state);
-}
-
 /**
  * writeback_in_progress - determine whether there is writeback in progress
  * @bdi: the device's backing_dev_info structure.
@@ -87,49 +62,11 @@ int writeback_in_progress(struct backing_dev_info *bdi)
         return !list_empty(&bdi->work_list);
 }
 
-static void bdi_work_free(struct rcu_head *head)
-{
-        struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);
-
-        clear_bit(WS_INPROGRESS, &work->state);
-        smp_mb__after_clear_bit();
-        wake_up_bit(&work->state, WS_INPROGRESS);
-
-        if (!test_bit(WS_ONSTACK, &work->state))
-                kfree(work);
-}
-
-static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
-{
-        /*
-         * The caller has retrieved the work arguments from this work,
-         * drop our reference. If this is the last ref, delete and free it
-         */
-        if (atomic_dec_and_test(&work->pending)) {
-                struct backing_dev_info *bdi = wb->bdi;
-
-                spin_lock(&bdi->wb_lock);
-                list_del_rcu(&work->list);
-                spin_unlock(&bdi->wb_lock);
-
-                call_rcu(&work->rcu_head, bdi_work_free);
-        }
-}
-
-static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
+static void bdi_queue_work(struct backing_dev_info *bdi,
+                struct wb_writeback_work *work)
 {
-        work->seen = bdi->wb_mask;
-        BUG_ON(!work->seen);
-        atomic_set(&work->pending, bdi->wb_cnt);
-        BUG_ON(!bdi->wb_cnt);
-
-        /*
-         * list_add_tail_rcu() contains the necessary barriers to
-         * make sure the above stores are seen before the item is
-         * noticed on the list
-         */
         spin_lock(&bdi->wb_lock);
-        list_add_tail_rcu(&work->list, &bdi->work_list);
+        list_add_tail(&work->list, &bdi->work_list);
         spin_unlock(&bdi->wb_lock);
 
         /*
@@ -146,55 +83,29 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
         }
 }
 
-/*
- * Used for on-stack allocated work items. The caller needs to wait until
- * the wb threads have acked the work before it's safe to continue.
- */
-static void bdi_wait_on_work_done(struct bdi_work *work)
-{
-        wait_on_bit(&work->state, WS_INPROGRESS, bdi_sched_wait,
-                    TASK_UNINTERRUPTIBLE);
-}
-
-static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
-                                 struct wb_writeback_args *args)
+static void
+__bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
+                bool range_cyclic, bool for_background)
 {
-        struct bdi_work *work;
+        struct wb_writeback_work *work;
 
         /*
          * This is WB_SYNC_NONE writeback, so if allocation fails just
          * wakeup the thread for old dirty data writeback
          */
-        work = kmalloc(sizeof(*work), GFP_ATOMIC);
-        if (work) {
-                bdi_work_init(work, args);
-                bdi_queue_work(bdi, work);
-        } else {
-                struct bdi_writeback *wb = &bdi->wb;
-
-                if (wb->task)
-                        wake_up_process(wb->task);
+        work = kzalloc(sizeof(*work), GFP_ATOMIC);
+        if (!work) {
+                if (bdi->wb.task)
+                        wake_up_process(bdi->wb.task);
+                return;
         }
-}
 
-/**
- * bdi_queue_work_onstack - start and wait for writeback
- * @args: parameters to control the work queue writeback
- *
- * Description:
- *   This function initiates writeback and waits for the operation to
- *   complete. Callers must hold the sb s_umount semaphore for
- *   reading, to avoid having the super disappear before we are done.
- */
-static void bdi_queue_work_onstack(struct wb_writeback_args *args)
-{
-        struct bdi_work work;
+        work->sync_mode = WB_SYNC_NONE;
+        work->nr_pages  = nr_pages;
+        work->range_cyclic = range_cyclic;
+        work->for_background = for_background;
 
-        bdi_work_init(&work, args);
-        __set_bit(WS_ONSTACK, &work.state);
-
-        bdi_queue_work(args->sb->s_bdi, &work);
-        bdi_wait_on_work_done(&work);
+        bdi_queue_work(bdi, work);
 }
 
 /**
@@ -210,13 +121,7 @@ static void bdi_queue_work_onstack(struct wb_writeback_args *args)
  */
 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
 {
-        struct wb_writeback_args args = {
-                .sync_mode      = WB_SYNC_NONE,
-                .nr_pages       = nr_pages,
-                .range_cyclic   = 1,
-        };
-
-        bdi_alloc_queue_work(bdi, &args);
+        __bdi_start_writeback(bdi, nr_pages, true, false);
 }
 
 /**
@@ -230,13 +135,7 @@ void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
  */
 void bdi_start_background_writeback(struct backing_dev_info *bdi)
 {
-        struct wb_writeback_args args = {
-                .sync_mode      = WB_SYNC_NONE,
-                .nr_pages       = LONG_MAX,
-                .for_background = 1,
-                .range_cyclic   = 1,
-        };
-        bdi_alloc_queue_work(bdi, &args);
+        __bdi_start_writeback(bdi, LONG_MAX, true, true);
 }
 
 /*
@@ -703,14 +602,14 @@ static inline bool over_bground_thresh(void)
  * all dirty pages if they are all attached to "old" mappings.
  */
 static long wb_writeback(struct bdi_writeback *wb,
-                         struct wb_writeback_args *args)
+                         struct wb_writeback_work *work)
 {
         struct writeback_control wbc = {
-                .sync_mode              = args->sync_mode,
+                .sync_mode              = work->sync_mode,
                 .older_than_this        = NULL,
-                .for_kupdate            = args->for_kupdate,
-                .for_background         = args->for_background,
-                .range_cyclic           = args->range_cyclic,
+                .for_kupdate            = work->for_kupdate,
+                .for_background         = work->for_background,
+                .range_cyclic           = work->range_cyclic,
         };
         unsigned long oldest_jif;
         long wrote = 0;
@@ -730,24 +629,24 @@ static long wb_writeback(struct bdi_writeback *wb,
                 /*
                  * Stop writeback when nr_pages has been consumed
                  */
-                if (args->nr_pages <= 0)
+                if (work->nr_pages <= 0)
                         break;
 
                 /*
                  * For background writeout, stop when we are below the
                  * background dirty threshold
                  */
-                if (args->for_background && !over_bground_thresh())
+                if (work->for_background && !over_bground_thresh())
                         break;
 
                 wbc.more_io = 0;
                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
                 wbc.pages_skipped = 0;
-                if (args->sb)
-                        __writeback_inodes_sb(args->sb, wb, &wbc);
+                if (work->sb)
+                        __writeback_inodes_sb(work->sb, wb, &wbc);
                 else
                         writeback_inodes_wb(wb, &wbc);
-                args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+                work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
                 wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 
                 /*
@@ -783,31 +682,21 @@ static long wb_writeback(struct bdi_writeback *wb,
 }
 
 /*
- * Return the next bdi_work struct that hasn't been processed by this
- * wb thread yet. ->seen is initially set for each thread that exists
- * for this device, when a thread first notices a piece of work it
- * clears its bit. Depending on writeback type, the thread will notify
- * completion on either receiving the work (WB_SYNC_NONE) or after
- * it is done (WB_SYNC_ALL).
+ * Return the next wb_writeback_work struct that hasn't been processed yet.
  */
-static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
-                                           struct bdi_writeback *wb)
+static struct wb_writeback_work *
+get_next_work_item(struct backing_dev_info *bdi, struct bdi_writeback *wb)
 {
-        struct bdi_work *work, *ret = NULL;
-
-        rcu_read_lock();
-
-        list_for_each_entry_rcu(work, &bdi->work_list, list) {
-                if (!test_bit(wb->nr, &work->seen))
-                        continue;
-                clear_bit(wb->nr, &work->seen);
+        struct wb_writeback_work *work = NULL;
 
-                ret = work;
-                break;
+        spin_lock(&bdi->wb_lock);
+        if (!list_empty(&bdi->work_list)) {
+                work = list_entry(bdi->work_list.next,
+                                  struct wb_writeback_work, list);
+                list_del_init(&work->list);
         }
-
-        rcu_read_unlock();
-        return ret;
+        spin_unlock(&bdi->wb_lock);
+        return work;
 }
 
 static long wb_check_old_data_flush(struct bdi_writeback *wb)
@@ -832,14 +721,14 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 
         if (nr_pages) {
-                struct wb_writeback_args args = {
+                struct wb_writeback_work work = {
                         .nr_pages       = nr_pages,
                         .sync_mode      = WB_SYNC_NONE,
                         .for_kupdate    = 1,
                         .range_cyclic   = 1,
                 };
 
-                return wb_writeback(wb, &args);
+                return wb_writeback(wb, &work);
         }
 
         return 0;
@@ -851,33 +740,27 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
 long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
 {
         struct backing_dev_info *bdi = wb->bdi;
-        struct bdi_work *work;
+        struct wb_writeback_work *work;
         long wrote = 0;
 
         while ((work = get_next_work_item(bdi, wb)) != NULL) {
-                struct wb_writeback_args args = work->args;
-
                 /*
                  * Override sync mode, in case we must wait for completion
+                 * because this thread is exiting now.
                  */
                 if (force_wait)
-                        work->args.sync_mode = args.sync_mode = WB_SYNC_ALL;
+                        work->sync_mode = WB_SYNC_ALL;
 
-                /*
-                 * If this isn't a data integrity operation, just notify
-                 * that we have seen this work and we are now starting it.
-                 */
-                if (!test_bit(WS_ONSTACK, &work->state))
-                        wb_clear_pending(wb, work);
-
-                wrote += wb_writeback(wb, &args);
+                wrote += wb_writeback(wb, work);
 
                 /*
-                 * This is a data integrity writeback, so only do the
-                 * notification when we have completed the work.
+                 * Notify the caller of completion if this is a synchronous
+                 * work item, otherwise just free it.
                  */
-                if (test_bit(WS_ONSTACK, &work->state))
-                        wb_clear_pending(wb, work);
+                if (work->done)
+                        complete(work->done);
+                else
+                        kfree(work);
         }
 
         /*
@@ -940,14 +823,9 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 void wakeup_flusher_threads(long nr_pages)
 {
         struct backing_dev_info *bdi;
-        struct wb_writeback_args args = {
-                .sync_mode      = WB_SYNC_NONE,
-        };
 
-        if (nr_pages) {
-                args.nr_pages = nr_pages;
-        } else {
-                args.nr_pages = global_page_state(NR_FILE_DIRTY) +
+        if (!nr_pages) {
+                nr_pages = global_page_state(NR_FILE_DIRTY) +
                                 global_page_state(NR_UNSTABLE_NFS);
         }
 
@@ -955,7 +833,7 @@ void wakeup_flusher_threads(long nr_pages)
         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
                 if (!bdi_has_dirty_io(bdi))
                         continue;
-                bdi_alloc_queue_work(bdi, &args);
+                __bdi_start_writeback(bdi, nr_pages, false, false);
         }
         rcu_read_unlock();
 }
@@ -1164,17 +1042,20 @@ void writeback_inodes_sb(struct super_block *sb)
 {
         unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
         unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
-        struct wb_writeback_args args = {
+        DECLARE_COMPLETION_ONSTACK(done);
+        struct wb_writeback_work work = {
                 .sb             = sb,
                 .sync_mode      = WB_SYNC_NONE,
+                .done           = &done,
         };
 
         WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-        args.nr_pages = nr_dirty + nr_unstable +
+        work.nr_pages = nr_dirty + nr_unstable +
                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 
-        bdi_queue_work_onstack(&args);
+        bdi_queue_work(sb->s_bdi, &work);
+        wait_for_completion(&done);
 }
 EXPORT_SYMBOL(writeback_inodes_sb);
 
@@ -1206,16 +1087,20 @@ EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
  */
 void sync_inodes_sb(struct super_block *sb)
 {
-        struct wb_writeback_args args = {
+        DECLARE_COMPLETION_ONSTACK(done);
+        struct wb_writeback_work work = {
                 .sb             = sb,
                 .sync_mode      = WB_SYNC_ALL,
                 .nr_pages       = LONG_MAX,
                 .range_cyclic   = 0,
+                .done           = &done,
         };
 
         WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-        bdi_queue_work_onstack(&args);
+        bdi_queue_work(sb->s_bdi, &work);
+        wait_for_completion(&done);
+
         wait_sb_inodes(sb);
 }
 EXPORT_SYMBOL(sync_inodes_sb);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 9ae2889096b6..e9aec0d099df 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -82,8 +82,6 @@ struct backing_dev_info {
         struct bdi_writeback wb;  /* default writeback info for this bdi */
         spinlock_t wb_lock;       /* protects update side of wb_list */
         struct list_head wb_list; /* the flusher threads hanging off this bdi */
-        unsigned long wb_mask;    /* bitmask of registered tasks */
-        unsigned int wb_cnt;      /* number of registered tasks */
 
         struct list_head work_list;
 
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 6e0b09a1ec2c..123bcef13e51 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -104,15 +104,13 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
                    "b_more_io:        %8lu\n"
                    "bdi_list:         %8u\n"
                    "state:            %8lx\n"
-                   "wb_mask:          %8lx\n"
-                   "wb_list:          %8u\n"
-                   "wb_cnt:           %8u\n",
+                   "wb_list:          %8u\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), nr_wb, nr_dirty, nr_io, nr_more_io,
-                   !list_empty(&bdi->bdi_list), bdi->state, bdi->wb_mask,
-                   !list_empty(&bdi->wb_list), bdi->wb_cnt);
+                   !list_empty(&bdi->bdi_list), bdi->state,
+                   !list_empty(&bdi->wb_list));
 #undef K
 
         return 0;
@@ -674,12 +672,6 @@ int bdi_init(struct backing_dev_info *bdi)
 
         bdi_wb_init(&bdi->wb, bdi);
 
-        /*
-         * Just one thread support for now, hard code mask and count
-         */
-        bdi->wb_mask = 1;
-        bdi->wb_cnt = 1;
-
         for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
                 err = percpu_counter_init(&bdi->bdi_stat[i], 0);
                 if (err)