Patch "block: discard bdi_unregister() in favour of bdi_destroy()" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

block: discard bdi_unregister() in favour of bdi_destroy()

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
block-discard-bdi_unregister-in-favour-of-bdi_destroy.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: NeilBrown <[email protected]>
Date: Tue, 19 May 2015 15:58:37 +1000
Subject: block: discard bdi_unregister() in favour of bdi_destroy()

From: NeilBrown <[email protected]>

commit aad653a0bc09dd4ebcb5579f9f835bbae9ef2ba3 upstream.

bdi_unregister() now contains very little functionality.

It contains a "WARN_ON" if bdi->dev is NULL. This warning is of no real consequence as bdi->dev isn't needed by anything else in the function, and it triggers if
blk_cleanup_queue() -> bdi_destroy()
is called before bdi_unregister, which happens since
Commit: 6cd18e711dd8 ("block: destroy bdi before blockdev is unregistered.")

So this isn't wanted.

It also calls bdi_set_min_ratio(). This needs to be called after writes through the bdi have all been flushed, and before the bdi is destroyed. Calling it early is better than calling it late as it frees up a global resource.

Calling it immediately after bdi_wb_shutdown() in bdi_destroy() perfectly fits these requirements.

So bdi_unregister() can be discarded with the important content moved to bdi_destroy(), as can the
writeback_bdi_unregister
event which is already not used.

---
 block/genhd.c                    |    1 -
 include/linux/backing-dev.h      |    1 -
 include/trace/events/writeback.h |    1 -
 mm/backing-dev.c                 |   18 +-----------------
 4 files changed, 1 insertion(+), 20 deletions(-)

@@ -653,7 +653,6 @@ void del_gendisk(struct gendisk *disk)
 	disk->flags &= ~GENHD_FL_UP;
 
 	sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
-	bdi_unregister(&disk->queue->backing_dev_info);
 	blk_unregister_queue(disk);
 	blk_unregister_region(disk_devt(disk), disk->minors);
 

@@ -116,7 +116,6 @@ __printf(3, 4)
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...);
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
-void bdi_unregister(struct backing_dev_info *bdi);
 int __must_check bdi_setup_and_register(struct backing_dev_info *, char *);
 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
 			enum wb_reason reason);

@@ -233,7 +233,6 @@ DEFINE_EVENT(writeback_class, name, \
 DEFINE_WRITEBACK_EVENT(writeback_nowork);
 DEFINE_WRITEBACK_EVENT(writeback_wake_background);
 DEFINE_WRITEBACK_EVENT(writeback_bdi_register);
-DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister);
 
 DECLARE_EVENT_CLASS(wbc_class,
 	TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi),

@@ -359,23 +359,6 @@ static void bdi_wb_shutdown(struct backi
 	flush_delayed_work(&bdi->wb.dwork);
 }
 
-/*
- * Called when the device behind @bdi has been removed or ejected.
- *
- * We can't really do much here except for reducing the dirty ratio at
- * the moment.  In the future we should be able to set a flag so that
- * the filesystem can handle errors at mark_inode_dirty time instead
- * of only at writeback time.
- */
-void bdi_unregister(struct backing_dev_info *bdi)
-{
-	if (WARN_ON_ONCE(!bdi->dev))
-		return;
-
-	bdi_set_min_ratio(bdi, 0);
-}
-EXPORT_SYMBOL(bdi_unregister);
-
 static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 {
 	memset(wb, 0, sizeof(*wb));

@@ -443,6 +426,7 @@ void bdi_destroy(struct backing_dev_info
 	int i;
 
 	bdi_wb_shutdown(bdi);
+	bdi_set_min_ratio(bdi, 0);
 
 	WARN_ON(!list_empty(&bdi->work_list));
 	WARN_ON(delayed_work_pending(&bdi->wb.dwork));

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/block-fix-ext_dev_lock-lockdep-report.patch queue-4.0/block-discard-bdi_unregister-in-favour-of-bdi_destroy.patch --
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