1 files changed, 156 insertions, 309 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1d1088f48bc2..d5be1693ac93 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -38,51 +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_* */
+        struct completion *done;        /* set if the caller waits */
 };
 
-enum {
-        WS_USED_B = 0,
-        WS_ONSTACK_B,
-};
-
-#define WS_USED (1 << WS_USED_B)
-#define WS_ONSTACK (1 << WS_ONSTACK_B)
-
-static inline bool bdi_work_on_stack(struct bdi_work *work)
-{
-        return test_bit(WS_ONSTACK_B, &work->state);
-}
-
-static inline void bdi_work_init(struct bdi_work *work,
-                                 struct wb_writeback_args *args)
-{
-        INIT_RCU_HEAD(&work->rcu_head);
-        work->args = *args;
-        work->state = WS_USED;
-}
-
 /**
  * writeback_in_progress - determine whether there is writeback in progress
  * @bdi: the device's backing_dev_info structure.
@@ -95,76 +62,11 @@ int writeback_in_progress(struct backing_dev_info *bdi)
         return !list_empty(&bdi->work_list);
 }
 
-static void bdi_work_clear(struct bdi_work *work)
-{
-        clear_bit(WS_USED_B, &work->state);
-        smp_mb__after_clear_bit();
-        /*
-         * work can have disappeared at this point. bit waitq functions
-         * should be able to tolerate this, provided bdi_sched_wait does
-         * not dereference it's pointer argument.
-        */
-        wake_up_bit(&work->state, WS_USED_B);
-}
-
-static void bdi_work_free(struct rcu_head *head)
-{
-        struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);
-
-        if (!bdi_work_on_stack(work))
-                kfree(work);
-        else
-                bdi_work_clear(work);
-}
-
-static void wb_work_complete(struct bdi_work *work)
-{
-        const enum writeback_sync_modes sync_mode = work->args.sync_mode;
-        int onstack = bdi_work_on_stack(work);
-
-        /*
-         * For allocated work, we can clear the done/seen bit right here.
-         * For on-stack work, we need to postpone both the clear and free
-         * to after the RCU grace period, since the stack could be invalidated
-         * as soon as bdi_work_clear() has done the wakeup.
-         */
-        if (!onstack)
-                bdi_work_clear(work);
-        if (sync_mode == WB_SYNC_NONE || onstack)
-                call_rcu(&work->rcu_head, bdi_work_free);
-}
-
-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);
-
-                wb_work_complete(work);
-        }
-}
-
-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);
 
         /*
@@ -181,97 +83,59 @@ 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_clear(struct bdi_work *work)
-{
-        wait_on_bit(&work->state, WS_USED_B, 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;
         }
+
+        work->sync_mode = WB_SYNC_NONE;
+        work->nr_pages  = nr_pages;
+        work->range_cyclic = range_cyclic;
+        work->for_background = for_background;
+
+        bdi_queue_work(bdi, work);
 }
 
 /**
- * bdi_sync_writeback - start and wait for writeback
+ * bdi_start_writeback - start writeback
  * @bdi: the backing device to write from
- * @sb: write inodes from this super_block
+ * @nr_pages: the number of pages to write
  *
  * Description:
- *   This does WB_SYNC_ALL data integrity writeback and waits for the
- *   IO to complete. Callers must hold the sb s_umount semaphore for
- *   reading, to avoid having the super disappear before we are done.
+ *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
+ *   started when this function returns, we make no guarentees on
+ *   completion. Caller need not hold sb s_umount semaphore.
+ *
  */
-static void bdi_sync_writeback(struct backing_dev_info *bdi,
-                               struct super_block *sb)
+void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
 {
-        struct wb_writeback_args args = {
-                .sb             = sb,
-                .sync_mode      = WB_SYNC_ALL,
-                .nr_pages       = LONG_MAX,
-                .range_cyclic   = 0,
-        };
-        struct bdi_work work;
-
-        bdi_work_init(&work, &args);
-        work.state |= WS_ONSTACK;
-
-        bdi_queue_work(bdi, &work);
-        bdi_wait_on_work_clear(&work);
+        __bdi_start_writeback(bdi, nr_pages, true, false);
 }
 
 /**
- * bdi_start_writeback - start writeback
+ * bdi_start_background_writeback - start background writeback
  * @bdi: the backing device to write from
- * @sb: write inodes from this super_block
- * @nr_pages: the number of pages to write
  *
  * Description:
- *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
+ *   This does WB_SYNC_NONE background writeback. The IO is only
  *   started when this function returns, we make no guarentees on
  *   completion. Caller need not hold sb s_umount semaphore.
- *
  */
-void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-                         long nr_pages)
+void bdi_start_background_writeback(struct backing_dev_info *bdi)
 {
-        struct wb_writeback_args args = {
-                .sb             = sb,
-                .sync_mode      = WB_SYNC_NONE,
-                .nr_pages       = nr_pages,
-                .range_cyclic   = 1,
-        };
-
-        /*
-         * We treat @nr_pages=0 as the special case to do background writeback,
-         * ie. to sync pages until the background dirty threshold is reached.
-         */
-        if (!nr_pages) {
-                args.nr_pages = LONG_MAX;
-                args.for_background = 1;
-        }
-
-        bdi_alloc_queue_work(bdi, &args);
+        __bdi_start_writeback(bdi, LONG_MAX, true, true);
 }
 
 /*
@@ -561,75 +425,69 @@ select_queue:
         return ret;
 }
 
-static void unpin_sb_for_writeback(struct super_block *sb)
-{
-        up_read(&sb->s_umount);
-        put_super(sb);
-}
-
-enum sb_pin_state {
-        SB_PINNED,
-        SB_NOT_PINNED,
-        SB_PIN_FAILED
-};
-
 /*
- * For WB_SYNC_NONE writeback, the caller does not have the sb pinned
+ * For background writeback the caller does not have the sb pinned
  * before calling writeback. So make sure that we do pin it, so it doesn't
  * go away while we are writing inodes from it.
  */
-static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc,
-                                              struct super_block *sb)
+static bool pin_sb_for_writeback(struct super_block *sb)
 {
-        /*
-         * Caller must already hold the ref for this
-         */
-        if (wbc->sync_mode == WB_SYNC_ALL) {
-                WARN_ON(!rwsem_is_locked(&sb->s_umount));
-                return SB_NOT_PINNED;
-        }
         spin_lock(&sb_lock);
+        if (list_empty(&sb->s_instances)) {
+                spin_unlock(&sb_lock);
+                return false;
+        }
+
         sb->s_count++;
+        spin_unlock(&sb_lock);
+
         if (down_read_trylock(&sb->s_umount)) {
-                if (sb->s_root) {
-                        spin_unlock(&sb_lock);
-                        return SB_PINNED;
-                }
-                /*
-                 * umounted, drop rwsem again and fall through to failure
-                 */
+                if (sb->s_root)
+                        return true;
                 up_read(&sb->s_umount);
         }
-        sb->s_count--;
-        spin_unlock(&sb_lock);
-        return SB_PIN_FAILED;
+
+        put_super(sb);
+        return false;
 }
 
 /*
  * Write a portion of b_io inodes which belong to @sb.
- * If @wbc->sb != NULL, then find and write all such
+ *
+ * If @only_this_sb is true, then find and write all such
  * inodes. Otherwise write only ones which go sequentially
  * in reverse order.
+ *
  * Return 1, if the caller writeback routine should be
  * interrupted. Otherwise return 0.
  */
-static int writeback_sb_inodes(struct super_block *sb,
-                               struct bdi_writeback *wb,
-                               struct writeback_control *wbc)
+static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
+                struct writeback_control *wbc, bool only_this_sb)
 {
         while (!list_empty(&wb->b_io)) {
                 long pages_skipped;
                 struct inode *inode = list_entry(wb->b_io.prev,
                                                  struct inode, i_list);
-                if (wbc->sb && sb != inode->i_sb) {
-                        /* super block given and doesn't
-                           match, skip this inode */
-                        redirty_tail(inode);
-                        continue;
-                }
-                if (sb != inode->i_sb)
-                        /* finish with this superblock */
+
+                if (inode->i_sb != sb) {
+                        if (only_this_sb) {
+                                /*
+                                 * We only want to write back data for this
+                                 * superblock, move all inodes not belonging
+                                 * to it back onto the dirty list.
+                                 */
+                                redirty_tail(inode);
+                                continue;
+                        }
+
+                        /*
+                         * The inode belongs to a different superblock.
+                         * Bounce back to the caller to unpin this and
+                         * pin the next superblock.
+                         */
                         return 0;
+                }
+
                 if (inode->i_state & (I_NEW | I_WILL_FREE)) {
                         requeue_io(inode);
                         continue;
@@ -667,8 +525,8 @@ static int writeback_sb_inodes(struct super_block *sb,
         return 1;
 }
 
-static void writeback_inodes_wb(struct bdi_writeback *wb,
-                                struct writeback_control *wbc)
+void writeback_inodes_wb(struct bdi_writeback *wb,
+                struct writeback_control *wbc)
 {
         int ret = 0;
 
@@ -681,24 +539,14 @@ static void writeback_inodes_wb(struct bdi_writeback *wb,
                 struct inode *inode = list_entry(wb->b_io.prev,
                                                  struct inode, i_list);
                 struct super_block *sb = inode->i_sb;
-                enum sb_pin_state state;
 
-                if (wbc->sb && sb != wbc->sb) {
-                        /* super block given and doesn't
-                           match, skip this inode */
-                        redirty_tail(inode);
-                        continue;
-                }
-                state = pin_sb_for_writeback(wbc, sb);
-
-                if (state == SB_PIN_FAILED) {
+                if (!pin_sb_for_writeback(sb)) {
                         requeue_io(inode);
                         continue;
                 }
-                ret = writeback_sb_inodes(sb, wb, wbc);
+                ret = writeback_sb_inodes(sb, wb, wbc, false);
+                drop_super(sb);
 
-                if (state == SB_PINNED)
-                        unpin_sb_for_writeback(sb);
                 if (ret)
                         break;
         }
@@ -706,11 +554,17 @@ static void writeback_inodes_wb(struct bdi_writeback *wb,
         /* Leave any unwritten inodes on b_io */
 }
 
-void writeback_inodes_wbc(struct writeback_control *wbc)
+static void __writeback_inodes_sb(struct super_block *sb,
+                struct bdi_writeback *wb, struct writeback_control *wbc)
 {
-        struct backing_dev_info *bdi = wbc->bdi;
+        WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-        writeback_inodes_wb(&bdi->wb, wbc);
+        wbc->wb_start = jiffies; /* livelock avoidance */
+        spin_lock(&inode_lock);
+        if (!wbc->for_kupdate || list_empty(&wb->b_io))
+                queue_io(wb, wbc->older_than_this);
+        writeback_sb_inodes(sb, wb, wbc, true);
+        spin_unlock(&inode_lock);
 }
 
 /*
@@ -748,16 +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 = {
-                .bdi                    = wb->bdi,
-                .sb                     = args->sb,
-                .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;
@@ -777,21 +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;
-                writeback_inodes_wb(wb, &wbc);
-                args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+                if (work->sb)
+                        __writeback_inodes_sb(work->sb, wb, &wbc);
+                else
+                        writeback_inodes_wb(wb, &wbc);
+                work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
                 wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 
                 /*
@@ -827,31 +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;
+        struct wb_writeback_work *work = 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);
-
-                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)
@@ -876,14 +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;
@@ -895,33 +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;
-
-                /*
-                 * If this isn't a data integrity operation, just notify
-                 * that we have seen this work and we are now starting it.
-                 */
-                if (args.sync_mode == WB_SYNC_NONE)
-                        wb_clear_pending(wb, work);
+                        work->sync_mode = WB_SYNC_ALL;
 
-                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 (args.sync_mode == WB_SYNC_ALL)
-                        wb_clear_pending(wb, work);
+                if (work->done)
+                        complete(work->done);
+                else
+                        kfree(work);
         }
 
         /*
@@ -978,42 +817,27 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 }
 
 /*
- * Schedule writeback for all backing devices. This does WB_SYNC_NONE
- * writeback, for integrity writeback see bdi_sync_writeback().
+ * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
+ * the whole world.
  */
-static void bdi_writeback_all(struct super_block *sb, long nr_pages)
+void wakeup_flusher_threads(long nr_pages)
 {
-        struct wb_writeback_args args = {
-                .sb             = sb,
-                .nr_pages       = nr_pages,
-                .sync_mode      = WB_SYNC_NONE,
-        };
         struct backing_dev_info *bdi;
 
-        rcu_read_lock();
+        if (!nr_pages) {
+                nr_pages = global_page_state(NR_FILE_DIRTY) +
+                                global_page_state(NR_UNSTABLE_NFS);
+        }
 
+        rcu_read_lock();
         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();
 }
 
-/*
- * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
- * the whole world.
- */
-void wakeup_flusher_threads(long nr_pages)
-{
-        if (nr_pages == 0)
-                nr_pages = global_page_state(NR_FILE_DIRTY) +
-                                global_page_state(NR_UNSTABLE_NFS);
-        bdi_writeback_all(NULL, nr_pages);
-}
-
 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
 {
         if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
@@ -1218,12 +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);
-        long nr_to_write;
+        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));
 
-        nr_to_write = nr_dirty + nr_unstable +
+        work.nr_pages = nr_dirty + nr_unstable +
                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 
-        bdi_start_writeback(sb->s_bdi, sb, nr_to_write);
+        bdi_queue_work(sb->s_bdi, &work);
+        wait_for_completion(&done);
 }
 EXPORT_SYMBOL(writeback_inodes_sb);
 
@@ -1237,7 +1069,9 @@ EXPORT_SYMBOL(writeback_inodes_sb);
 int writeback_inodes_sb_if_idle(struct super_block *sb)
 {
         if (!writeback_in_progress(sb->s_bdi)) {
+                down_read(&sb->s_umount);
                 writeback_inodes_sb(sb);
+                up_read(&sb->s_umount);
                 return 1;
         } else
                 return 0;
@@ -1253,7 +1087,20 @@ EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
  */
 void sync_inodes_sb(struct super_block *sb)
 {
-        bdi_sync_writeback(sb->s_bdi, sb);
+        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(sb->s_bdi, &work);
+        wait_for_completion(&done);
+
         wait_sb_inodes(sb);
 }
 EXPORT_SYMBOL(sync_inodes_sb);