From aa5cbd103887011b4830355f88fb055f9ad2d556 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Mon, 14 Dec 2009 12:49:46 +1100
Subject: md/bitmap: protect against bitmap removal while being updated.

A write intent bitmap can be removed from an array while the
array is active.
When this happens, all IO is suspended and flushed before the
bitmap is removed.
However it is possible that bitmap_daemon_work is still running to
clear old bits from the bitmap.  If it is, it can dereference the
bitmap after it has been freed.

So introduce a new mutex to protect bitmap_daemon_work and get it
before destroying a bitmap.

This is suitable for any current -stable kernel.

Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 60e2b32..a5e5f2f 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1078,23 +1078,31 @@ static bitmap_counter_t *bitmap_get_counter(struct bitmap *bitmap,
  *			out to disk
  */
 
-void bitmap_daemon_work(struct bitmap *bitmap)
+void bitmap_daemon_work(mddev_t *mddev)
 {
+	struct bitmap *bitmap;
 	unsigned long j;
 	unsigned long flags;
 	struct page *page = NULL, *lastpage = NULL;
 	int blocks;
 	void *paddr;
 
-	if (bitmap == NULL)
+	/* Use a mutex to guard daemon_work against
+	 * bitmap_destroy.
+	 */
+	mutex_lock(&mddev->bitmap_mutex);
+	bitmap = mddev->bitmap;
+	if (bitmap == NULL) {
+		mutex_unlock(&mddev->bitmap_mutex);
 		return;
+	}
 	if (time_before(jiffies, bitmap->daemon_lastrun + bitmap->daemon_sleep*HZ))
 		goto done;
 
 	bitmap->daemon_lastrun = jiffies;
 	if (bitmap->allclean) {
 		bitmap->mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
-		return;
+		goto done;
 	}
 	bitmap->allclean = 1;
 
@@ -1203,6 +1211,7 @@ void bitmap_daemon_work(struct bitmap *bitmap)
  done:
 	if (bitmap->allclean == 0)
 		bitmap->mddev->thread->timeout = bitmap->daemon_sleep * HZ;
+	mutex_unlock(&mddev->bitmap_mutex);
 }
 
 static bitmap_counter_t *bitmap_get_counter(struct bitmap *bitmap,
@@ -1541,9 +1550,9 @@ void bitmap_flush(mddev_t *mddev)
 	 */
 	sleep = bitmap->daemon_sleep;
 	bitmap->daemon_sleep = 0;
-	bitmap_daemon_work(bitmap);
-	bitmap_daemon_work(bitmap);
-	bitmap_daemon_work(bitmap);
+	bitmap_daemon_work(mddev);
+	bitmap_daemon_work(mddev);
+	bitmap_daemon_work(mddev);
 	bitmap->daemon_sleep = sleep;
 	bitmap_update_sb(bitmap);
 }
@@ -1574,6 +1583,7 @@ static void bitmap_free(struct bitmap *bitmap)
 	kfree(bp);
 	kfree(bitmap);
 }
+
 void bitmap_destroy(mddev_t *mddev)
 {
 	struct bitmap *bitmap = mddev->bitmap;
@@ -1581,7 +1591,9 @@ void bitmap_destroy(mddev_t *mddev)
 	if (!bitmap) /* there was no bitmap */
 		return;
 
+	mutex_lock(&mddev->bitmap_mutex);
 	mddev->bitmap = NULL; /* disconnect from the md device */
+	mutex_unlock(&mddev->bitmap_mutex);
 	if (mddev->thread)
 		mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
 
diff --git a/drivers/md/bitmap.h b/drivers/md/bitmap.h
index e989006..7e38d13 100644
--- a/drivers/md/bitmap.h
+++ b/drivers/md/bitmap.h
@@ -282,7 +282,7 @@ void bitmap_close_sync(struct bitmap *bitmap);
 void bitmap_cond_end_sync(struct bitmap *bitmap, sector_t sector);
 
 void bitmap_unplug(struct bitmap *bitmap);
-void bitmap_daemon_work(struct bitmap *bitmap);
+void bitmap_daemon_work(mddev_t *mddev);
 #endif
 
 #endif
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 5f154ef..1be7a16 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -363,6 +363,7 @@ static mddev_t * mddev_find(dev_t unit)
 
 	mutex_init(&new->open_mutex);
 	mutex_init(&new->reconfig_mutex);
+	mutex_init(&new->bitmap_mutex);
 	INIT_LIST_HEAD(&new->disks);
 	INIT_LIST_HEAD(&new->all_mddevs);
 	init_timer(&new->safemode_timer);
@@ -6625,7 +6626,7 @@ void md_check_recovery(mddev_t *mddev)
 
 
 	if (mddev->bitmap)
-		bitmap_daemon_work(mddev->bitmap);
+		bitmap_daemon_work(mddev);
 
 	if (mddev->ro)
 		return;
diff --git a/drivers/md/md.h b/drivers/md/md.h
index f184b69..87430fe 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -289,6 +289,7 @@ struct mddev_s
 								* hot-adding a bitmap.  It should
 								* eventually be settable by sysfs.
 								*/
+	struct mutex			bitmap_mutex;
 
 	struct list_head		all_mddevs;
 };
-- 
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