From 7eaceaccab5f40bbfda044629a6298616aeaed50 Mon Sep 17 00:00:00 2001
From: Jens Axboe <jaxboe@fusionio.com>
Date: Thu, 10 Mar 2011 08:52:07 +0100
Subject: block: remove per-queue plugging

Code has been converted over to the new explicit on-stack plugging,
and delay users have been converted to use the new API for that.
So lets kill off the old plugging along with aops->sync_page().

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
---
 mm/backing-dev.c    |  6 -----
 mm/filemap.c        | 67 +++++------------------------------------------------
 mm/memory-failure.c |  8 +++----
 mm/nommu.c          |  4 ----
 mm/page-writeback.c |  2 +-
 mm/readahead.c      | 12 ----------
 mm/shmem.c          |  1 -
 mm/swap_state.c     |  5 +---
 mm/swapfile.c       | 37 -----------------------------
 mm/vmscan.c         |  2 +-
 10 files changed, 13 insertions(+), 131 deletions(-)

(limited to 'mm')

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 027100d3022..c91e139a652 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -14,17 +14,11 @@
 
 static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
 
-void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
-{
-}
-EXPORT_SYMBOL(default_unplug_io_fn);
-
 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,
-	.unplug_io_fn	= default_unplug_io_fn,
 };
 EXPORT_SYMBOL_GPL(default_backing_dev_info);
 
diff --git a/mm/filemap.c b/mm/filemap.c
index 83a45d35468..380776c2a9a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -155,45 +155,15 @@ void remove_from_page_cache(struct page *page)
 }
 EXPORT_SYMBOL(remove_from_page_cache);
 
-static int sync_page(void *word)
+static int sleep_on_page(void *word)
 {
-	struct address_space *mapping;
-	struct page *page;
-
-	page = container_of((unsigned long *)word, struct page, flags);
-
-	/*
-	 * page_mapping() is being called without PG_locked held.
-	 * Some knowledge of the state and use of the page is used to
-	 * reduce the requirements down to a memory barrier.
-	 * The danger here is of a stale page_mapping() return value
-	 * indicating a struct address_space different from the one it's
-	 * associated with when it is associated with one.
-	 * After smp_mb(), it's either the correct page_mapping() for
-	 * the page, or an old page_mapping() and the page's own
-	 * page_mapping() has gone NULL.
-	 * The ->sync_page() address_space operation must tolerate
-	 * page_mapping() going NULL. By an amazing coincidence,
-	 * this comes about because none of the users of the page
-	 * in the ->sync_page() methods make essential use of the
-	 * page_mapping(), merely passing the page down to the backing
-	 * device's unplug functions when it's non-NULL, which in turn
-	 * ignore it for all cases but swap, where only page_private(page) is
-	 * of interest. When page_mapping() does go NULL, the entire
-	 * call stack gracefully ignores the page and returns.
-	 * -- wli
-	 */
-	smp_mb();
-	mapping = page_mapping(page);
-	if (mapping && mapping->a_ops && mapping->a_ops->sync_page)
-		mapping->a_ops->sync_page(page);
 	io_schedule();
 	return 0;
 }
 
-static int sync_page_killable(void *word)
+static int sleep_on_page_killable(void *word)
 {
-	sync_page(word);
+	sleep_on_page(word);
 	return fatal_signal_pending(current) ? -EINTR : 0;
 }
 
@@ -479,12 +449,6 @@ struct page *__page_cache_alloc(gfp_t gfp)
 EXPORT_SYMBOL(__page_cache_alloc);
 #endif
 
-static int __sleep_on_page_lock(void *word)
-{
-	io_schedule();
-	return 0;
-}
-
 /*
  * In order to wait for pages to become available there must be
  * waitqueues associated with pages. By using a hash table of
@@ -512,7 +476,7 @@ void wait_on_page_bit(struct page *page, int bit_nr)
 	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
 
 	if (test_bit(bit_nr, &page->flags))
-		__wait_on_bit(page_waitqueue(page), &wait, sync_page,
+		__wait_on_bit(page_waitqueue(page), &wait, sleep_on_page,
 							TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(wait_on_page_bit);
@@ -576,17 +540,12 @@ EXPORT_SYMBOL(end_page_writeback);
 /**
  * __lock_page - get a lock on the page, assuming we need to sleep to get it
  * @page: the page to lock
- *
- * Ugly. Running sync_page() in state TASK_UNINTERRUPTIBLE is scary.  If some
- * random driver's requestfn sets TASK_RUNNING, we could busywait.  However
- * chances are that on the second loop, the block layer's plug list is empty,
- * so sync_page() will then return in state TASK_UNINTERRUPTIBLE.
  */
 void __lock_page(struct page *page)
 {
 	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
 
-	__wait_on_bit_lock(page_waitqueue(page), &wait, sync_page,
+	__wait_on_bit_lock(page_waitqueue(page), &wait, sleep_on_page,
 							TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(__lock_page);
@@ -596,24 +555,10 @@ int __lock_page_killable(struct page *page)
 	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
 
 	return __wait_on_bit_lock(page_waitqueue(page), &wait,
-					sync_page_killable, TASK_KILLABLE);
+					sleep_on_page_killable, TASK_KILLABLE);
 }
 EXPORT_SYMBOL_GPL(__lock_page_killable);
 
-/**
- * __lock_page_nosync - get a lock on the page, without calling sync_page()
- * @page: the page to lock
- *
- * Variant of lock_page that does not require the caller to hold a reference
- * on the page's mapping.
- */
-void __lock_page_nosync(struct page *page)
-{
-	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
-	__wait_on_bit_lock(page_waitqueue(page), &wait, __sleep_on_page_lock,
-							TASK_UNINTERRUPTIBLE);
-}
-
 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
 			 unsigned int flags)
 {
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 0207c2f6f8b..bfba796d374 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -945,7 +945,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 		collect_procs(ppage, &tokill);
 
 	if (hpage != ppage)
-		lock_page_nosync(ppage);
+		lock_page(ppage);
 
 	ret = try_to_unmap(ppage, ttu);
 	if (ret != SWAP_SUCCESS)
@@ -1038,7 +1038,7 @@ int __memory_failure(unsigned long pfn, int trapno, int flags)
 			 * Check "just unpoisoned", "filter hit", and
 			 * "race with other subpage."
 			 */
-			lock_page_nosync(hpage);
+			lock_page(hpage);
 			if (!PageHWPoison(hpage)
 			    || (hwpoison_filter(p) && TestClearPageHWPoison(p))
 			    || (p != hpage && TestSetPageHWPoison(hpage))) {
@@ -1088,7 +1088,7 @@ int __memory_failure(unsigned long pfn, int trapno, int flags)
 	 * It's very difficult to mess with pages currently under IO
 	 * and in many cases impossible, so we just avoid it here.
 	 */
-	lock_page_nosync(hpage);
+	lock_page(hpage);
 
 	/*
 	 * unpoison always clear PG_hwpoison inside page lock
@@ -1231,7 +1231,7 @@ int unpoison_memory(unsigned long pfn)
 		return 0;
 	}
 
-	lock_page_nosync(page);
+	lock_page(page);
 	/*
 	 * This test is racy because PG_hwpoison is set outside of page lock.
 	 * That's acceptable because that won't trigger kernel panic. Instead,
diff --git a/mm/nommu.c b/mm/nommu.c
index f59e1424d3d..fb6cbd6abe1 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1842,10 +1842,6 @@ int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
 }
 EXPORT_SYMBOL(remap_vmalloc_range);
 
-void swap_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
-{
-}
-
 unsigned long arch_get_unmapped_area(struct file *file, unsigned long addr,
 	unsigned long len, unsigned long pgoff, unsigned long flags)
 {
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2cb01f6ec5d..cc0ede169e4 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1239,7 +1239,7 @@ int set_page_dirty_lock(struct page *page)
 {
 	int ret;
 
-	lock_page_nosync(page);
+	lock_page(page);
 	ret = set_page_dirty(page);
 	unlock_page(page);
 	return ret;
diff --git a/mm/readahead.c b/mm/readahead.c
index 77506a291a2..cbddc3e1724 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -554,17 +554,5 @@ page_cache_async_readahead(struct address_space *mapping,
 
 	/* do read-ahead */
 	ondemand_readahead(mapping, ra, filp, true, offset, req_size);
-
-#ifdef CONFIG_BLOCK
-	/*
-	 * Normally the current page is !uptodate and lock_page() will be
-	 * immediately called to implicitly unplug the device. However this
-	 * is not always true for RAID conifgurations, where data arrives
-	 * not strictly in their submission order. In this case we need to
-	 * explicitly kick off the IO.
-	 */
-	if (PageUptodate(page))
-		blk_run_backing_dev(mapping->backing_dev_info, NULL);
-#endif
 }
 EXPORT_SYMBOL_GPL(page_cache_async_readahead);
diff --git a/mm/shmem.c b/mm/shmem.c
index 5ee67c99060..24d23f5bedf 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -224,7 +224,6 @@ static const struct vm_operations_struct shmem_vm_ops;
 static struct backing_dev_info shmem_backing_dev_info  __read_mostly = {
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
-	.unplug_io_fn	= default_unplug_io_fn,
 };
 
 static LIST_HEAD(shmem_swaplist);
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 5c8cfabbc9b..46680461785 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -24,12 +24,10 @@
 
 /*
  * swapper_space is a fiction, retained to simplify the path through
- * vmscan's shrink_page_list, to make sync_page look nicer, and to allow
- * future use of radix_tree tags in the swap cache.
+ * vmscan's shrink_page_list.
  */
 static const struct address_space_operations swap_aops = {
 	.writepage	= swap_writepage,
-	.sync_page	= block_sync_page,
 	.set_page_dirty	= __set_page_dirty_nobuffers,
 	.migratepage	= migrate_page,
 };
@@ -37,7 +35,6 @@ static const struct address_space_operations swap_aops = {
 static struct backing_dev_info swap_backing_dev_info = {
 	.name		= "swap",
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
-	.unplug_io_fn	= swap_unplug_io_fn,
 };
 
 struct address_space swapper_space = {
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 07a458d72fa..7ceea78ceb2 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -94,39 +94,6 @@ __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
 	return ret;
 }
 
-/*
- * We need this because the bdev->unplug_fn can sleep and we cannot
- * hold swap_lock while calling the unplug_fn. And swap_lock
- * cannot be turned into a mutex.
- */
-static DECLARE_RWSEM(swap_unplug_sem);
-
-void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
-{
-	swp_entry_t entry;
-
-	down_read(&swap_unplug_sem);
-	entry.val = page_private(page);
-	if (PageSwapCache(page)) {
-		struct block_device *bdev = swap_info[swp_type(entry)]->bdev;
-		struct backing_dev_info *bdi;
-
-		/*
-		 * If the page is removed from swapcache from under us (with a
-		 * racy try_to_unuse/swapoff) we need an additional reference
-		 * count to avoid reading garbage from page_private(page) above.
-		 * If the WARN_ON triggers during a swapoff it maybe the race
-		 * condition and it's harmless. However if it triggers without
-		 * swapoff it signals a problem.
-		 */
-		WARN_ON(page_count(page) <= 1);
-
-		bdi = bdev->bd_inode->i_mapping->backing_dev_info;
-		blk_run_backing_dev(bdi, page);
-	}
-	up_read(&swap_unplug_sem);
-}
-
 /*
  * swapon tell device that all the old swap contents can be discarded,
  * to allow the swap device to optimize its wear-levelling.
@@ -1643,10 +1610,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 		goto out_dput;
 	}
 
-	/* wait for any unplug function to finish */
-	down_write(&swap_unplug_sem);
-	up_write(&swap_unplug_sem);
-
 	destroy_swap_extents(p);
 	if (p->flags & SWP_CONTINUED)
 		free_swap_count_continuations(p);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 17497d0cd8b..251bed73ac0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -358,7 +358,7 @@ static int may_write_to_queue(struct backing_dev_info *bdi,
 static void handle_write_error(struct address_space *mapping,
 				struct page *page, int error)
 {
-	lock_page_nosync(page);
+	lock_page(page);
 	if (page_mapping(page) == mapping)
 		mapping_set_error(mapping, error);
 	unlock_page(page);
-- 
cgit v1.2.3-70-g09d2


From 55602dd66f5353981b53f734e26c307f310ced37 Mon Sep 17 00:00:00 2001
From: Jens Axboe <jaxboe@fusionio.com>
Date: Thu, 24 Jun 2010 15:05:37 +0200
Subject: fs: make generic file read/write functions plug

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
---
 mm/filemap.c | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'mm')

diff --git a/mm/filemap.c b/mm/filemap.c
index 380776c2a9a..f9a29c87a2c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1243,12 +1243,15 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 	unsigned long seg = 0;
 	size_t count;
 	loff_t *ppos = &iocb->ki_pos;
+	struct blk_plug plug;
 
 	count = 0;
 	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
 	if (retval)
 		return retval;
 
+	blk_start_plug(&plug);
+
 	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
 	if (filp->f_flags & O_DIRECT) {
 		loff_t size;
@@ -1321,6 +1324,7 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 			break;
 	}
 out:
+	blk_finish_plug(&plug);
 	return retval;
 }
 EXPORT_SYMBOL(generic_file_aio_read);
@@ -2432,11 +2436,13 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file->f_mapping->host;
+	struct blk_plug plug;
 	ssize_t ret;
 
 	BUG_ON(iocb->ki_pos != pos);
 
 	mutex_lock(&inode->i_mutex);
+	blk_start_plug(&plug);
 	ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
 	mutex_unlock(&inode->i_mutex);
 
@@ -2447,6 +2453,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 		if (err < 0 && ret > 0)
 			ret = err;
 	}
+	blk_finish_plug(&plug);
 	return ret;
 }
 EXPORT_SYMBOL(generic_file_aio_write);
-- 
cgit v1.2.3-70-g09d2


From 5b417b1873694ece3291d7f64a943304559a817b Mon Sep 17 00:00:00 2001
From: Jens Axboe <jaxboe@fusionio.com>
Date: Mon, 19 Apr 2010 10:04:38 +0200
Subject: read-ahead: use plugging

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
---
 mm/readahead.c | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'mm')

diff --git a/mm/readahead.c b/mm/readahead.c
index cbddc3e1724..2c0cc489e28 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -109,9 +109,12 @@ EXPORT_SYMBOL(read_cache_pages);
 static int read_pages(struct address_space *mapping, struct file *filp,
 		struct list_head *pages, unsigned nr_pages)
 {
+	struct blk_plug plug;
 	unsigned page_idx;
 	int ret;
 
+	blk_start_plug(&plug);
+
 	if (mapping->a_ops->readpages) {
 		ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
 		/* Clean up the remaining pages */
@@ -129,7 +132,10 @@ static int read_pages(struct address_space *mapping, struct file *filp,
 		page_cache_release(page);
 	}
 	ret = 0;
+
 out:
+	blk_finish_plug(&plug);
+
 	return ret;
 }
 
-- 
cgit v1.2.3-70-g09d2


From 721a9602e6607417c6bc15b18e97a2f35266c690 Mon Sep 17 00:00:00 2001
From: Jens Axboe <jaxboe@fusionio.com>
Date: Wed, 9 Mar 2011 11:56:30 +0100
Subject: block: kill off REQ_UNPLUG

With the plugging now being explicitly controlled by the
submitter, callers need not pass down unplugging hints
to the block layer. If they want to unplug, it's because they
manually plugged on their own - in which case, they should just
unplug at will.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
---
 block/blk-core.c                   |  2 +-
 drivers/block/drbd/drbd_actlog.c   |  2 +-
 drivers/block/drbd/drbd_int.h      |  2 +-
 drivers/block/drbd/drbd_main.c     |  3 +--
 drivers/block/drbd/drbd_receiver.c |  9 +--------
 drivers/md/bitmap.c                |  2 +-
 drivers/md/dm-io.c                 |  2 +-
 drivers/md/dm-kcopyd.c             |  5 +----
 drivers/md/md.c                    |  5 ++---
 fs/btrfs/extent_io.c               |  2 +-
 fs/buffer.c                        | 14 ++++----------
 fs/direct-io.c                     |  2 +-
 fs/ext4/page-io.c                  |  3 +--
 fs/gfs2/log.c                      |  4 ++--
 fs/gfs2/lops.c                     | 12 ++++++------
 fs/gfs2/meta_io.c                  |  2 +-
 fs/jbd/commit.c                    |  2 +-
 fs/jbd2/commit.c                   |  6 +++---
 fs/nilfs2/segbuf.c                 |  2 +-
 fs/xfs/linux-2.6/xfs_aops.c        |  3 +--
 include/linux/blk_types.h          |  2 --
 include/linux/fs.h                 | 28 +++++++++-------------------
 kernel/power/block_io.c            |  2 +-
 mm/page_io.c                       |  2 +-
 24 files changed, 43 insertions(+), 75 deletions(-)

(limited to 'mm')

diff --git a/block/blk-core.c b/block/blk-core.c
index 82a45898ba7..7e9715ae18c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1290,7 +1290,7 @@ get_rq:
 	}
 
 	plug = current->plug;
-	if (plug && !sync) {
+	if (plug) {
 		if (!plug->should_sort && !list_empty(&plug->list)) {
 			struct request *__rq;
 
diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 2096628d6e6..aca302492ff 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -80,7 +80,7 @@ static int _drbd_md_sync_page_io(struct drbd_conf *mdev,
 
 	if ((rw & WRITE) && !test_bit(MD_NO_FUA, &mdev->flags))
 		rw |= REQ_FUA;
-	rw |= REQ_UNPLUG | REQ_SYNC;
+	rw |= REQ_SYNC;
 
 	bio = bio_alloc(GFP_NOIO, 1);
 	bio->bi_bdev = bdev->md_bdev;
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 0b5718e1958..b0bd27dfc1e 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -377,7 +377,7 @@ union p_header {
 #define DP_HARDBARRIER	      1 /* depricated */
 #define DP_RW_SYNC	      2 /* equals REQ_SYNC    */
 #define DP_MAY_SET_IN_SYNC    4
-#define DP_UNPLUG             8 /* equals REQ_UNPLUG  */
+#define DP_UNPLUG             8 /* not used anymore   */
 #define DP_FUA               16 /* equals REQ_FUA     */
 #define DP_FLUSH             32 /* equals REQ_FLUSH   */
 #define DP_DISCARD           64 /* equals REQ_DISCARD */
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 6049cb85310..8a43ce0edee 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2477,12 +2477,11 @@ static u32 bio_flags_to_wire(struct drbd_conf *mdev, unsigned long bi_rw)
 {
 	if (mdev->agreed_pro_version >= 95)
 		return  (bi_rw & REQ_SYNC ? DP_RW_SYNC : 0) |
-			(bi_rw & REQ_UNPLUG ? DP_UNPLUG : 0) |
 			(bi_rw & REQ_FUA ? DP_FUA : 0) |
 			(bi_rw & REQ_FLUSH ? DP_FLUSH : 0) |
 			(bi_rw & REQ_DISCARD ? DP_DISCARD : 0);
 	else
-		return bi_rw & (REQ_SYNC | REQ_UNPLUG) ? DP_RW_SYNC : 0;
+		return bi_rw & REQ_SYNC ? DP_RW_SYNC : 0;
 }
 
 /* Used to send write requests
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 84132f8bf8a..8e68be939de 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -1100,8 +1100,6 @@ next_bio:
 	/* > e->sector, unless this is the first bio */
 	bio->bi_sector = sector;
 	bio->bi_bdev = mdev->ldev->backing_bdev;
-	/* we special case some flags in the multi-bio case, see below
-	 * (REQ_UNPLUG) */
 	bio->bi_rw = rw;
 	bio->bi_private = e;
 	bio->bi_end_io = drbd_endio_sec;
@@ -1130,10 +1128,6 @@ next_bio:
 		bios = bios->bi_next;
 		bio->bi_next = NULL;
 
-		/* strip off REQ_UNPLUG unless it is the last bio */
-		if (bios)
-			bio->bi_rw &= ~REQ_UNPLUG;
-
 		drbd_generic_make_request(mdev, fault_type, bio);
 	} while (bios);
 	return 0;
@@ -1621,12 +1615,11 @@ static unsigned long write_flags_to_bio(struct drbd_conf *mdev, u32 dpf)
 {
 	if (mdev->agreed_pro_version >= 95)
 		return  (dpf & DP_RW_SYNC ? REQ_SYNC : 0) |
-			(dpf & DP_UNPLUG ? REQ_UNPLUG : 0) |
 			(dpf & DP_FUA ? REQ_FUA : 0) |
 			(dpf & DP_FLUSH ? REQ_FUA : 0) |
 			(dpf & DP_DISCARD ? REQ_DISCARD : 0);
 	else
-		return dpf & DP_RW_SYNC ? (REQ_SYNC | REQ_UNPLUG) : 0;
+		return dpf & DP_RW_SYNC ? REQ_SYNC : 0;
 }
 
 /* mirrored write */
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 54bfc274b39..ca203cb23f3 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -347,7 +347,7 @@ static void write_page(struct bitmap *bitmap, struct page *page, int wait)
 			atomic_inc(&bitmap->pending_writes);
 			set_buffer_locked(bh);
 			set_buffer_mapped(bh);
-			submit_bh(WRITE | REQ_UNPLUG | REQ_SYNC, bh);
+			submit_bh(WRITE | REQ_SYNC, bh);
 			bh = bh->b_this_page;
 		}
 
diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 136d4f71a11..76a5af00a26 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -352,7 +352,7 @@ static void dispatch_io(int rw, unsigned int num_regions,
 	BUG_ON(num_regions > DM_IO_MAX_REGIONS);
 
 	if (sync)
-		rw |= REQ_SYNC | REQ_UNPLUG;
+		rw |= REQ_SYNC;
 
 	/*
 	 * For multiple regions we need to be careful to rewind
diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c
index 400cf35094a..1bb73a13ca4 100644
--- a/drivers/md/dm-kcopyd.c
+++ b/drivers/md/dm-kcopyd.c
@@ -356,11 +356,8 @@ static int run_io_job(struct kcopyd_job *job)
 
 	if (job->rw == READ)
 		r = dm_io(&io_req, 1, &job->source, NULL);
-	else {
-		if (job->num_dests > 1)
-			io_req.bi_rw |= REQ_UNPLUG;
+	else
 		r = dm_io(&io_req, job->num_dests, job->dests, NULL);
-	}
 
 	return r;
 }
diff --git a/drivers/md/md.c b/drivers/md/md.c
index ca0d79c264b..28f9c1ee4e3 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -777,8 +777,7 @@ void md_super_write(mddev_t *mddev, mdk_rdev_t *rdev,
 	bio->bi_end_io = super_written;
 
 	atomic_inc(&mddev->pending_writes);
-	submit_bio(REQ_WRITE | REQ_SYNC | REQ_UNPLUG | REQ_FLUSH | REQ_FUA,
-		   bio);
+	submit_bio(REQ_WRITE | REQ_SYNC | REQ_FLUSH | REQ_FUA, bio);
 }
 
 void md_super_wait(mddev_t *mddev)
@@ -806,7 +805,7 @@ int sync_page_io(mdk_rdev_t *rdev, sector_t sector, int size,
 	struct completion event;
 	int ret;
 
-	rw |= REQ_SYNC | REQ_UNPLUG;
+	rw |= REQ_SYNC;
 
 	bio->bi_bdev = (metadata_op && rdev->meta_bdev) ?
 		rdev->meta_bdev : rdev->bdev;
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 92ac5192c51..b76f7cd4740 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2182,7 +2182,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 	unsigned long nr_written = 0;
 
 	if (wbc->sync_mode == WB_SYNC_ALL)
-		write_flags = WRITE_SYNC_PLUG;
+		write_flags = WRITE_SYNC;
 	else
 		write_flags = WRITE;
 
diff --git a/fs/buffer.c b/fs/buffer.c
index f903f2e5b4f..42534f67d71 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -767,7 +767,7 @@ static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
 				 * still in flight on potentially older
 				 * contents.
 				 */
-				write_dirty_buffer(bh, WRITE_SYNC_PLUG);
+				write_dirty_buffer(bh, WRITE_SYNC);
 
 				/*
 				 * Kick off IO for the previous mapping. Note
@@ -1602,14 +1602,8 @@ EXPORT_SYMBOL(unmap_underlying_metadata);
  * prevents this contention from occurring.
  *
  * If block_write_full_page() is called with wbc->sync_mode ==
- * WB_SYNC_ALL, the writes are posted using WRITE_SYNC_PLUG; this
- * causes the writes to be flagged as synchronous writes, but the
- * block device queue will NOT be unplugged, since usually many pages
- * will be pushed to the out before the higher-level caller actually
- * waits for the writes to be completed.  The various wait functions,
- * such as wait_on_writeback_range() will ultimately call sync_page()
- * which will ultimately call blk_run_backing_dev(), which will end up
- * unplugging the device queue.
+ * WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
+ * causes the writes to be flagged as synchronous writes.
  */
 static int __block_write_full_page(struct inode *inode, struct page *page,
 			get_block_t *get_block, struct writeback_control *wbc,
@@ -1622,7 +1616,7 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
 	const unsigned blocksize = 1 << inode->i_blkbits;
 	int nr_underway = 0;
 	int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
-			WRITE_SYNC_PLUG : WRITE);
+			WRITE_SYNC : WRITE);
 
 	BUG_ON(!PageLocked(page));
 
diff --git a/fs/direct-io.c b/fs/direct-io.c
index df709b3b860..42608313609 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1173,7 +1173,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	struct dio *dio;
 
 	if (rw & WRITE)
-		rw = WRITE_ODIRECT_PLUG;
+		rw = WRITE_ODIRECT;
 
 	if (bdev)
 		bdev_blkbits = blksize_bits(bdev_logical_block_size(bdev));
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 955cc309142..e2cd90e4bb7 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -310,8 +310,7 @@ static int io_submit_init(struct ext4_io_submit *io,
 	io_end->offset = (page->index << PAGE_CACHE_SHIFT) + bh_offset(bh);
 
 	io->io_bio = bio;
-	io->io_op = (wbc->sync_mode == WB_SYNC_ALL ?
-			WRITE_SYNC_PLUG : WRITE);
+	io->io_op = (wbc->sync_mode == WB_SYNC_ALL ?  WRITE_SYNC : WRITE);
 	io->io_next_block = bh->b_blocknr;
 	return 0;
 }
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index eb01f3575e1..7f1c1120234 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -121,7 +121,7 @@ __acquires(&sdp->sd_log_lock)
 			lock_buffer(bh);
 			if (test_clear_buffer_dirty(bh)) {
 				bh->b_end_io = end_buffer_write_sync;
-				submit_bh(WRITE_SYNC_PLUG, bh);
+				submit_bh(WRITE_SYNC, bh);
 			} else {
 				unlock_buffer(bh);
 				brelse(bh);
@@ -647,7 +647,7 @@ static void gfs2_ordered_write(struct gfs2_sbd *sdp)
 		lock_buffer(bh);
 		if (buffer_mapped(bh) && test_clear_buffer_dirty(bh)) {
 			bh->b_end_io = end_buffer_write_sync;
-			submit_bh(WRITE_SYNC_PLUG, bh);
+			submit_bh(WRITE_SYNC, bh);
 		} else {
 			unlock_buffer(bh);
 			brelse(bh);
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index bf33f822058..48b545a1979 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -200,7 +200,7 @@ static void buf_lo_before_commit(struct gfs2_sbd *sdp)
 		}
 
 		gfs2_log_unlock(sdp);
-		submit_bh(WRITE_SYNC_PLUG, bh);
+		submit_bh(WRITE_SYNC, bh);
 		gfs2_log_lock(sdp);
 
 		n = 0;
@@ -210,7 +210,7 @@ static void buf_lo_before_commit(struct gfs2_sbd *sdp)
 			gfs2_log_unlock(sdp);
 			lock_buffer(bd2->bd_bh);
 			bh = gfs2_log_fake_buf(sdp, bd2->bd_bh);
-			submit_bh(WRITE_SYNC_PLUG, bh);
+			submit_bh(WRITE_SYNC, bh);
 			gfs2_log_lock(sdp);
 			if (++n >= num)
 				break;
@@ -352,7 +352,7 @@ static void revoke_lo_before_commit(struct gfs2_sbd *sdp)
 		sdp->sd_log_num_revoke--;
 
 		if (offset + sizeof(u64) > sdp->sd_sb.sb_bsize) {
-			submit_bh(WRITE_SYNC_PLUG, bh);
+			submit_bh(WRITE_SYNC, bh);
 
 			bh = gfs2_log_get_buf(sdp);
 			mh = (struct gfs2_meta_header *)bh->b_data;
@@ -369,7 +369,7 @@ static void revoke_lo_before_commit(struct gfs2_sbd *sdp)
 	}
 	gfs2_assert_withdraw(sdp, !sdp->sd_log_num_revoke);
 
-	submit_bh(WRITE_SYNC_PLUG, bh);
+	submit_bh(WRITE_SYNC, bh);
 }
 
 static void revoke_lo_before_scan(struct gfs2_jdesc *jd,
@@ -571,7 +571,7 @@ static void gfs2_write_blocks(struct gfs2_sbd *sdp, struct buffer_head *bh,
 	ptr = bh_log_ptr(bh);
 	
 	get_bh(bh);
-	submit_bh(WRITE_SYNC_PLUG, bh);
+	submit_bh(WRITE_SYNC, bh);
 	gfs2_log_lock(sdp);
 	while(!list_empty(list)) {
 		bd = list_entry(list->next, struct gfs2_bufdata, bd_le.le_list);
@@ -597,7 +597,7 @@ static void gfs2_write_blocks(struct gfs2_sbd *sdp, struct buffer_head *bh,
 		} else {
 			bh1 = gfs2_log_fake_buf(sdp, bd->bd_bh);
 		}
-		submit_bh(WRITE_SYNC_PLUG, bh1);
+		submit_bh(WRITE_SYNC, bh1);
 		gfs2_log_lock(sdp);
 		ptr += 2;
 	}
diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index a566331db4e..867b713cba9 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -37,7 +37,7 @@ static int gfs2_aspace_writepage(struct page *page, struct writeback_control *wb
 	struct buffer_head *bh, *head;
 	int nr_underway = 0;
 	int write_op = REQ_META |
-		(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC_PLUG : WRITE);
+		(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);
 
 	BUG_ON(!PageLocked(page));
 	BUG_ON(!page_has_buffers(page));
diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index 34a4861c14b..66be299acb1 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -333,7 +333,7 @@ void journal_commit_transaction(journal_t *journal)
 	 * instead we rely on sync_buffer() doing the unplug for us.
 	 */
 	if (commit_transaction->t_synchronous_commit)
-		write_op = WRITE_SYNC_PLUG;
+		write_op = WRITE_SYNC;
 	spin_lock(&commit_transaction->t_handle_lock);
 	while (commit_transaction->t_updates) {
 		DEFINE_WAIT(wait);
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index f3ad1598b20..3da1cc4346d 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -137,9 +137,9 @@ static int journal_submit_commit_record(journal_t *journal,
 	if (journal->j_flags & JBD2_BARRIER &&
 	    !JBD2_HAS_INCOMPAT_FEATURE(journal,
 				       JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT))
-		ret = submit_bh(WRITE_SYNC_PLUG | WRITE_FLUSH_FUA, bh);
+		ret = submit_bh(WRITE_SYNC | WRITE_FLUSH_FUA, bh);
 	else
-		ret = submit_bh(WRITE_SYNC_PLUG, bh);
+		ret = submit_bh(WRITE_SYNC, bh);
 
 	*cbh = bh;
 	return ret;
@@ -369,7 +369,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	 * instead we rely on sync_buffer() doing the unplug for us.
 	 */
 	if (commit_transaction->t_synchronous_commit)
-		write_op = WRITE_SYNC_PLUG;
+		write_op = WRITE_SYNC;
 	trace_jbd2_commit_locking(journal, commit_transaction);
 	stats.run.rs_wait = commit_transaction->t_max_wait;
 	stats.run.rs_locked = jiffies;
diff --git a/fs/nilfs2/segbuf.c b/fs/nilfs2/segbuf.c
index 0f83e93935b..2853ff20f85 100644
--- a/fs/nilfs2/segbuf.c
+++ b/fs/nilfs2/segbuf.c
@@ -509,7 +509,7 @@ static int nilfs_segbuf_write(struct nilfs_segment_buffer *segbuf,
 		 * Last BIO is always sent through the following
 		 * submission.
 		 */
-		rw |= REQ_SYNC | REQ_UNPLUG;
+		rw |= REQ_SYNC;
 		res = nilfs_segbuf_submit_bio(segbuf, &wi, rw);
 	}
 
diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index 83c1c20d145..6bbb0ee3325 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -413,8 +413,7 @@ xfs_submit_ioend_bio(
 	if (xfs_ioend_new_eof(ioend))
 		xfs_mark_inode_dirty(XFS_I(ioend->io_inode));
 
-	submit_bio(wbc->sync_mode == WB_SYNC_ALL ?
-		   WRITE_SYNC_PLUG : WRITE, bio);
+	submit_bio(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE, bio);
 }
 
 STATIC struct bio *
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 16b28647304..be50d9e70a7 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -128,7 +128,6 @@ enum rq_flag_bits {
 	__REQ_NOIDLE,		/* don't anticipate more IO after this one */
 
 	/* bio only flags */
-	__REQ_UNPLUG,		/* unplug the immediately after submission */
 	__REQ_RAHEAD,		/* read ahead, can fail anytime */
 	__REQ_THROTTLED,	/* This bio has already been subjected to
 				 * throttling rules. Don't do it again. */
@@ -172,7 +171,6 @@ enum rq_flag_bits {
 	 REQ_NOIDLE | REQ_FLUSH | REQ_FUA)
 #define REQ_CLONE_MASK		REQ_COMMON_MASK
 
-#define REQ_UNPLUG		(1 << __REQ_UNPLUG)
 #define REQ_RAHEAD		(1 << __REQ_RAHEAD)
 #define REQ_THROTTLED		(1 << __REQ_THROTTLED)
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9f2cf69911b..543e226ea6a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -135,16 +135,10 @@ struct inodes_stat_t {
  *			block layer could (in theory) choose to ignore this
  *			request if it runs into resource problems.
  * WRITE		A normal async write. Device will be plugged.
- * WRITE_SYNC_PLUG	Synchronous write. Identical to WRITE, but passes down
+ * WRITE_SYNC		Synchronous write. Identical to WRITE, but passes down
  *			the hint that someone will be waiting on this IO
- *			shortly. The device must still be unplugged explicitly,
- *			WRITE_SYNC_PLUG does not do this as we could be
- *			submitting more writes before we actually wait on any
- *			of them.
- * WRITE_SYNC		Like WRITE_SYNC_PLUG, but also unplugs the device
- *			immediately after submission. The write equivalent
- *			of READ_SYNC.
- * WRITE_ODIRECT_PLUG	Special case write for O_DIRECT only.
+ *			shortly. The write equivalent of READ_SYNC.
+ * WRITE_ODIRECT	Special case write for O_DIRECT only.
  * WRITE_FLUSH		Like WRITE_SYNC but with preceding cache flush.
  * WRITE_FUA		Like WRITE_SYNC but data is guaranteed to be on
  *			non-volatile media on completion.
@@ -160,18 +154,14 @@ struct inodes_stat_t {
 #define WRITE			RW_MASK
 #define READA			RWA_MASK
 
-#define READ_SYNC		(READ | REQ_SYNC | REQ_UNPLUG)
+#define READ_SYNC		(READ | REQ_SYNC)
 #define READ_META		(READ | REQ_META)
-#define WRITE_SYNC_PLUG		(WRITE | REQ_SYNC | REQ_NOIDLE)
-#define WRITE_SYNC		(WRITE | REQ_SYNC | REQ_NOIDLE | REQ_UNPLUG)
-#define WRITE_ODIRECT_PLUG	(WRITE | REQ_SYNC)
+#define WRITE_SYNC		(WRITE | REQ_SYNC | REQ_NOIDLE)
+#define WRITE_ODIRECT		(WRITE | REQ_SYNC)
 #define WRITE_META		(WRITE | REQ_META)
-#define WRITE_FLUSH		(WRITE | REQ_SYNC | REQ_NOIDLE | REQ_UNPLUG | \
-				 REQ_FLUSH)
-#define WRITE_FUA		(WRITE | REQ_SYNC | REQ_NOIDLE | REQ_UNPLUG | \
-				 REQ_FUA)
-#define WRITE_FLUSH_FUA		(WRITE | REQ_SYNC | REQ_NOIDLE | REQ_UNPLUG | \
-				 REQ_FLUSH | REQ_FUA)
+#define WRITE_FLUSH		(WRITE | REQ_SYNC | REQ_NOIDLE | REQ_FLUSH)
+#define WRITE_FUA		(WRITE | REQ_SYNC | REQ_NOIDLE | REQ_FUA)
+#define WRITE_FLUSH_FUA		(WRITE | REQ_SYNC | REQ_NOIDLE | REQ_FLUSH | REQ_FUA)
 
 #define SEL_IN		1
 #define SEL_OUT		2
diff --git a/kernel/power/block_io.c b/kernel/power/block_io.c
index 83bbc7c02df..d09dd10c5a5 100644
--- a/kernel/power/block_io.c
+++ b/kernel/power/block_io.c
@@ -28,7 +28,7 @@
 static int submit(int rw, struct block_device *bdev, sector_t sector,
 		struct page *page, struct bio **bio_chain)
 {
-	const int bio_rw = rw | REQ_SYNC | REQ_UNPLUG;
+	const int bio_rw = rw | REQ_SYNC;
 	struct bio *bio;
 
 	bio = bio_alloc(__GFP_WAIT | __GFP_HIGH, 1);
diff --git a/mm/page_io.c b/mm/page_io.c
index 2dee975bf46..dc76b4d0611 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -106,7 +106,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		goto out;
 	}
 	if (wbc->sync_mode == WB_SYNC_ALL)
-		rw |= REQ_SYNC | REQ_UNPLUG;
+		rw |= REQ_SYNC;
 	count_vm_event(PSWPOUT);
 	set_page_writeback(page);
 	unlock_page(page);
-- 
cgit v1.2.3-70-g09d2


From 9b6096a65f99a89dfd8328c4e469e7b53b3ae04a Mon Sep 17 00:00:00 2001
From: Shaohua Li <shaohua.li@intel.com>
Date: Thu, 17 Mar 2011 10:47:06 +0100
Subject: mm: make generic_writepages() use plugging

This recovers a performance regression caused by the removal
of the per-device plugging.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
---
 mm/page-writeback.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

(limited to 'mm')

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index cc0ede169e4..24b7ac2bc36 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1039,11 +1039,17 @@ static int __writepage(struct page *page, struct writeback_control *wbc,
 int generic_writepages(struct address_space *mapping,
 		       struct writeback_control *wbc)
 {
+	struct blk_plug plug;
+	int ret;
+
 	/* deal with chardevs and other special file */
 	if (!mapping->a_ops->writepage)
 		return 0;
 
-	return write_cache_pages(mapping, wbc, __writepage, mapping);
+	blk_start_plug(&plug);
+	ret = write_cache_pages(mapping, wbc, __writepage, mapping);
+	blk_finish_plug(&plug);
+	return ret;
 }
 
 EXPORT_SYMBOL(generic_writepages);
-- 
cgit v1.2.3-70-g09d2


From 95f28604a65b1c40b6c6cd95e58439cd7ded3add Mon Sep 17 00:00:00 2001
From: Jens Axboe <jaxboe@fusionio.com>
Date: Thu, 17 Mar 2011 11:13:12 +0100
Subject: fs: assign sb->s_bdi to default_backing_dev_info if the bdi is going
 away

We don't have proper reference counting for this yet, so we run into
cases where the device is pulled and we OOPS on flushing the fs data.
This happens even though the dirty inodes have already been
migrated to the default_backing_dev_info.

Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Tested-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
---
 fs/super.c       | 2 ++
 fs/sync.c        | 4 ++--
 mm/backing-dev.c | 2 +-
 3 files changed, 5 insertions(+), 3 deletions(-)

(limited to 'mm')

diff --git a/fs/super.c b/fs/super.c
index 7e9dd4cc2c0..0d89e93f654 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -71,6 +71,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
 #else
 		INIT_LIST_HEAD(&s->s_files);
 #endif
+		s->s_bdi = &default_backing_dev_info;
 		INIT_LIST_HEAD(&s->s_instances);
 		INIT_HLIST_BL_HEAD(&s->s_anon);
 		INIT_LIST_HEAD(&s->s_inodes);
@@ -1003,6 +1004,7 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
 	}
 	BUG_ON(!mnt->mnt_sb);
 	WARN_ON(!mnt->mnt_sb->s_bdi);
+	WARN_ON(mnt->mnt_sb->s_bdi == &default_backing_dev_info);
 	mnt->mnt_sb->s_flags |= MS_BORN;
 
 	error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
diff --git a/fs/sync.c b/fs/sync.c
index ba76b9623e7..412dc89163d 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -33,7 +33,7 @@ static int __sync_filesystem(struct super_block *sb, int wait)
 	 * This should be safe, as we require bdi backing to actually
 	 * write out data in the first place
 	 */
-	if (!sb->s_bdi || sb->s_bdi == &noop_backing_dev_info)
+	if (sb->s_bdi == &noop_backing_dev_info)
 		return 0;
 
 	if (sb->s_qcop && sb->s_qcop->quota_sync)
@@ -79,7 +79,7 @@ EXPORT_SYMBOL_GPL(sync_filesystem);
 
 static void sync_one_sb(struct super_block *sb, void *arg)
 {
-	if (!(sb->s_flags & MS_RDONLY) && sb->s_bdi)
+	if (!(sb->s_flags & MS_RDONLY))
 		__sync_filesystem(sb, *(int *)arg);
 }
 /*
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index c91e139a652..8fe9d340792 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -598,7 +598,7 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
 	spin_lock(&sb_lock);
 	list_for_each_entry(sb, &super_blocks, s_list) {
 		if (sb->s_bdi == bdi)
-			sb->s_bdi = NULL;
+			sb->s_bdi = &default_backing_dev_info;
 	}
 	spin_unlock(&sb_lock);
 }
-- 
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