Merge branch 'linus' into core/rcu

Conflicts:
	fs/fs-writeback.c

Merge reason: Resolve the conflict

Note, i picked the version from Linus's tree, which effectively reverts
the fs-writeback.c bits of:

  b97181f: fs: remove all rcu head initializations, except on_stack initializations

As the upstream changes to this file changed this code heavily and the
first attempt to resolve the conflict resulted in a non-booting kernel.
It's safer to re-try this portion of the commit cleanly.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 109 insertions, 170 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index af92100a7411..0609607d3955 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -63,45 +63,16 @@ struct bdi_work {
 };
 
 enum {
-        WS_USED_B = 0,
-        WS_ONSTACK_B,
+        WS_INPROGRESS = 0,
+        WS_ONSTACK,
 };
 
-#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,
-                                   int on_stack)
-{
-        work->args = *args;
-        work->state = WS_USED;
-        if (on_stack) {
-                work->state |= WS_ONSTACK;
-                init_rcu_head_on_stack(&work->rcu_head);
-        }
-}
-
 static inline void bdi_work_init(struct bdi_work *work,
                                  struct wb_writeback_args *args)
 {
-        __bdi_work_init(work, args, false);
-}
-
-static inline void bdi_work_init_on_stack(struct bdi_work *work,
-                                          struct wb_writeback_args *args)
-{
-        __bdi_work_init(work, args, true);
-}
-
-static inline void bdi_destroy_work_on_stack(struct bdi_work *work)
-{
-        destroy_rcu_head_on_stack(&work->rcu_head);
+        INIT_RCU_HEAD(&work->rcu_head);
+        work->args = *args;
+        __set_bit(WS_INPROGRESS, &work->state);
 }
 
 /**
@@ -116,43 +87,16 @@ 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);
+        clear_bit(WS_INPROGRESS, &work->state);
+        smp_mb__after_clear_bit();
+        wake_up_bit(&work->state, WS_INPROGRESS);
 
-        /*
-         * 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);
+        if (!test_bit(WS_ONSTACK, &work->state))
+                kfree(work);
 }
 
 static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
@@ -168,7 +112,7 @@ static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
                 list_del_rcu(&work->list);
                 spin_unlock(&bdi->wb_lock);
 
-                wb_work_complete(work);
+                call_rcu(&work->rcu_head, bdi_work_free);
         }
 }
 
@@ -206,9 +150,9 @@ 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)
+static void bdi_wait_on_work_done(struct bdi_work *work)
 {
-        wait_on_bit(&work->state, WS_USED_B, bdi_sched_wait,
+        wait_on_bit(&work->state, WS_INPROGRESS, bdi_sched_wait,
                     TASK_UNINTERRUPTIBLE);
 }
 
@@ -234,37 +178,28 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
 }
 
 /**
- * bdi_sync_writeback - start and wait for writeback
- * @bdi: the backing device to write from
+ * bdi_queue_work_onstack - start and wait for writeback
  * @sb: write inodes from this super_block
  *
  * 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
+ *   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_sync_writeback(struct backing_dev_info *bdi,
-                               struct super_block *sb)
+static void bdi_queue_work_onstack(struct wb_writeback_args *args)
 {
-        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_on_stack(&work, &args);
+        bdi_work_init(&work, args);
+        __set_bit(WS_ONSTACK, &work.state);
 
-        bdi_queue_work(bdi, &work);
-        bdi_wait_on_work_clear(&work);
-        bdi_destroy_work_on_stack(&work);
+        bdi_queue_work(args->sb->s_bdi, &work);
+        bdi_wait_on_work_done(&work);
 }
 
 /**
  * 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:
@@ -273,25 +208,34 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
  *   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_writeback(struct backing_dev_info *bdi, long nr_pages)
 {
         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_background_writeback - start background writeback
+ * @bdi: the backing device to write from
+ *
+ * Description:
+ *   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_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);
 }
 
@@ -582,48 +526,30 @@ 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;
 }
 
 /*
@@ -702,24 +628,31 @@ 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 (wbc->sb) {
+                        /*
+                         * We are requested to write out inodes for a specific
+                         * superblock.  This means we already have s_umount
+                         * taken by the caller which also waits for us to
+                         * complete the writeout.
+                         */
+                        if (sb != wbc->sb) {
+                                redirty_tail(inode);
+                                continue;
+                        }
 
-                if (state == SB_PIN_FAILED) {
-                        requeue_io(inode);
-                        continue;
+                        WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+                        ret = writeback_sb_inodes(sb, wb, wbc);
+                } else {
+                        if (!pin_sb_for_writeback(sb)) {
+                                requeue_io(inode);
+                                continue;
+                        }
+                        ret = writeback_sb_inodes(sb, wb, wbc);
+                        drop_super(sb);
                 }
-                ret = writeback_sb_inodes(sb, wb, wbc);
 
-                if (state == SB_PINNED)
-                        unpin_sb_for_writeback(sb);
                 if (ret)
                         break;
         }
@@ -932,7 +865,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
                  * 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)
+                if (!test_bit(WS_ONSTACK, &work->state))
                         wb_clear_pending(wb, work);
 
                 wrote += wb_writeback(wb, &args);
@@ -941,7 +874,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
                  * This is a data integrity writeback, so only do the
                  * notification when we have completed the work.
                  */
-                if (args.sync_mode == WB_SYNC_ALL)
+                if (test_bit(WS_ONSTACK, &work->state))
                         wb_clear_pending(wb, work);
         }
 
@@ -999,42 +932,32 @@ 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 backing_dev_info *bdi;
         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) {
+                args.nr_pages = nr_pages;
+        } else {
+                args.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);
         }
-
         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")) {
@@ -1239,12 +1162,17 @@ 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;
+        struct wb_writeback_args args = {
+                .sb             = sb,
+                .sync_mode      = WB_SYNC_NONE,
+        };
 
-        nr_to_write = nr_dirty + nr_unstable +
+        WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+        args.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_onstack(&args);
 }
 EXPORT_SYMBOL(writeback_inodes_sb);
 
@@ -1258,7 +1186,9 @@ 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;
@@ -1274,7 +1204,16 @@ EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
  */
 void sync_inodes_sb(struct super_block *sb)
 {
-        bdi_sync_writeback(sb->s_bdi, sb);
+        struct wb_writeback_args args = {
+                .sb             = sb,
+                .sync_mode      = WB_SYNC_ALL,
+                .nr_pages       = LONG_MAX,
+                .range_cyclic   = 0,
+        };
+
+        WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+        bdi_queue_work_onstack(&args);
         wait_sb_inodes(sb);
 }
 EXPORT_SYMBOL(sync_inodes_sb);