Merge branch 'for-3.19/core' of git://git.kernel.dk/linux-block

Pull block driver core update from Jens Axboe:
 "This is the pull request for the core block IO changes for 3.19.  Not
  a huge round this time, mostly lots of little good fixes:

   - Fix a bug in sysfs blktrace interface causing a NULL pointer
     dereference, when enabled/disabled through that API.  From Arianna
     Avanzini.

   - Various updates/fixes/improvements for blk-mq:

        - A set of updates from Bart, mostly fixing buts in the tag
          handling.

        - Cleanup/code consolidation from Christoph.

        - Extend queue_rq API to be able to handle batching issues of IO
          requests. NVMe will utilize this shortly. From me.

        - A few tag and request handling updates from me.

        - Cleanup of the preempt handling for running queues from Paolo.

        - Prevent running of unmapped hardware queues from Ming Lei.

        - Move the kdump memory limiting check to be in the correct
          location, from Shaohua.

        - Initialize all software queues at init time from Takashi. This
          prevents a kobject warning when CPUs are brought online that
          weren't online when a queue was registered.

   - Single writeback fix for I_DIRTY clearing from Tejun.  Queued with
     the core IO changes, since it's just a single fix.

   - Version X of the __bio_add_page() segment addition retry from
     Maurizio.  Hope the Xth time is the charm.

   - Documentation fixup for IO scheduler merging from Jan.

   - Introduce (and use) generic IO stat accounting helpers for non-rq
     drivers, from Gu Zheng.

   - Kill off artificial limiting of max sectors in a request from
     Christoph"

* 'for-3.19/core' of git://git.kernel.dk/linux-block: (26 commits)
  bio: modify __bio_add_page() to accept pages that don't start a new segment
  blk-mq: Fix uninitialized kobject at CPU hotplugging
  blktrace: don't let the sysfs interface remove trace from running list
  blk-mq: Use all available hardware queues
  blk-mq: Micro-optimize bt_get()
  blk-mq: Fix a race between bt_clear_tag() and bt_get()
  blk-mq: Avoid that __bt_get_word() wraps multiple times
  blk-mq: Fix a use-after-free
  blk-mq: prevent unmapped hw queue from being scheduled
  blk-mq: re-check for available tags after running the hardware queue
  blk-mq: fix hang in bt_get()
  blk-mq: move the kdump check to blk_mq_alloc_tag_set
  blk-mq: cleanup tag free handling
  blk-mq: use 'nr_cpu_ids' as highest CPU ID count for hwq <-> cpu map
  blk: introduce generic io stat accounting help function
  blk-mq: handle the single queue case in blk_mq_hctx_next_cpu
  genhd: check for int overflow in disk_expand_part_tbl()
  blk-mq: add blk_mq_free_hctx_request()
  blk-mq: export blk_mq_free_request()
  blk-mq: use get_cpu/put_cpu instead of preempt_disable/preempt_enable
  ...

1 files changed, 22 insertions, 7 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index ef9bef118342..2d609a5fbfea 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -479,12 +479,28 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
          * write_inode()
          */
         spin_lock(&inode->i_lock);
-        /* Clear I_DIRTY_PAGES if we've written out all dirty pages */
-        if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
-                inode->i_state &= ~I_DIRTY_PAGES;
+
         dirty = inode->i_state & I_DIRTY;
-        inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
+        inode->i_state &= ~I_DIRTY;
+
+        /*
+         * Paired with smp_mb() in __mark_inode_dirty().  This allows
+         * __mark_inode_dirty() to test i_state without grabbing i_lock -
+         * either they see the I_DIRTY bits cleared or we see the dirtied
+         * inode.
+         *
+         * I_DIRTY_PAGES is always cleared together above even if @mapping
+         * still has dirty pages.  The flag is reinstated after smp_mb() if
+         * necessary.  This guarantees that either __mark_inode_dirty()
+         * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
+         */
+        smp_mb();
+
+        if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
+                inode->i_state |= I_DIRTY_PAGES;
+
         spin_unlock(&inode->i_lock);
+
         /* Don't write the inode if only I_DIRTY_PAGES was set */
         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
                 int err = write_inode(inode, wbc);
@@ -1148,12 +1164,11 @@ void __mark_inode_dirty(struct inode *inode, int flags)
         }
 
         /*
-         * make sure that changes are seen by all cpus before we test i_state
-         * -- mikulas
+         * Paired with smp_mb() in __writeback_single_inode() for the
+         * following lockless i_state test.  See there for details.
          */
         smp_mb();
 
-        /* avoid the locking if we can */
         if ((inode->i_state & flags) == flags)
                 return;