Message-ID: <20130130155718.GB1272@konrad-lan.dumpdata.com>
Date:	Wed, 30 Jan 2013 10:57:18 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	sjenning@...ux.vnet.ibm.com, dan.magenheimer@...cle.com,
	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, ngupta@...are.org, minchan@...nel.org,
	mgorman@...e.de, fschmaus@...il.com, andor.daam@...glemail.com,
	ilendir@...glemail.com
Subject: Re: [PATCH 1/8] mm: cleancache: lazy initialization to allow tmem
 backends to build/run as modules

On Fri, Nov 16, 2012 at 03:10:49PM -0800, Andrew Morton wrote:
> On Wed, 14 Nov 2012 13:57:05 -0500
> Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> 
> > From: Dan Magenheimer <dan.magenheimer@...cle.com>
> > 
> > With the goal of allowing tmem backends (zcache, ramster, Xen tmem) to be
> > built/loaded as modules rather than built-in and enabled by a boot parameter,
> > this patch provides "lazy initialization", allowing backends to register to
> > cleancache even after filesystems were mounted. Calls to init_fs and
> > init_shared_fs are remembered as fake poolids but no real tmem_pools created.
> > On backend registration the fake poolids are mapped to real poolids and
> > respective tmem_pools.
> 
> What is your merge plan/path for this work?
> 
> >
> > ...
> >
> > + * When no backend is registered all calls to init_fs and init_shard_fs
> 
> "init_shared_fs"
> 
> > + * are registered and fake poolids are given to the respective
> > + * super block but no tmem_pools are created. When a backend
> > + * registers with cleancache the previous calls to init_fs and
> > + * init_shared_fs are executed to create tmem_pools and set the
> > + * respective poolids. While no backend is registered all "puts",
> > + * "gets" and "flushes" are ignored or fail.
> 
> The comment could use all 80 cols..
> 
> >
> > ...
> >
> >  struct cleancache_ops cleancache_register_ops(struct cleancache_ops *ops)
> >  {
> >  	struct cleancache_ops old = cleancache_ops;
> > +	int i;
> >  
> >  	cleancache_ops = *ops;
> > -	cleancache_enabled = 1;
> > +
> > +	backend_registered = true;
> > +	for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
> > +		if (fs_poolid_map[i] == FS_NO_BACKEND)
> > +			fs_poolid_map[i] = (*cleancache_ops.init_fs)(PAGE_SIZE);
> > +		if (shared_fs_poolid_map[i] == FS_NO_BACKEND)
> > +			shared_fs_poolid_map[i] = (*cleancache_ops.init_shared_fs)
> > +					(uuids[i], PAGE_SIZE);
> > +	}
> >  	return old;
> >  }
> 
> I never noticed before - this function returns a large structure by
> value.  That's really really unusual in the kernel.  I see no problem
> with it per-se, but it might generate awful code.
> 
> Also, this function has no locking and is blatantly racy.
> 
> >  EXPORT_SYMBOL(cleancache_register_ops);
> > @@ -61,15 +91,38 @@ EXPORT_SYMBOL(cleancache_register_ops);
> >  /* Called by a cleancache-enabled filesystem at time of mount */
> >  void __cleancache_init_fs(struct super_block *sb)
> >  {
> > -	sb->cleancache_poolid = (*cleancache_ops.init_fs)(PAGE_SIZE);
> > +	int i;
> > +
> > +	for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
> > +		if (fs_poolid_map[i] == FS_UNKNOWN) {
> > +			sb->cleancache_poolid = i + FAKE_FS_POOLID_OFFSET;
> > +			if (backend_registered)
> > +				fs_poolid_map[i] = (*cleancache_ops.init_fs)(PAGE_SIZE);
> > +			else
> > +				fs_poolid_map[i] = FS_NO_BACKEND;
> > +			break;
> > +		}
> > +	}
> >  }
> >  EXPORT_SYMBOL(__cleancache_init_fs);
> 
> This also looks wildly racy.
> 
> >  /* Called by a cleancache-enabled clustered filesystem at time of mount */
> >  void __cleancache_init_shared_fs(char *uuid, struct super_block *sb)
> >  {
> > -	sb->cleancache_poolid =
> > -		(*cleancache_ops.init_shared_fs)(uuid, PAGE_SIZE);
> > +	int i;
> > +
> > +	for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
> > +		if (shared_fs_poolid_map[i] == FS_UNKNOWN) {
> > +			sb->cleancache_poolid = i + FAKE_SHARED_FS_POOLID_OFFSET;
> > +			uuids[i] = uuid;
> > +			if (backend_registered)
> > +				shared_fs_poolid_map[i] = (*cleancache_ops.init_shared_fs)
> > +						(uuid, PAGE_SIZE);
> > +			else
> > +				shared_fs_poolid_map[i] = FS_NO_BACKEND;
> > +			break;
> > +		}
> > +	}
> >  }
> >  EXPORT_SYMBOL(__cleancache_init_shared_fs);
> 
> Again, a huge mess if two threads execute this concurrently.
> 
> > @@ -99,6 +152,19 @@ static int cleancache_get_key(struct inode *inode,
> >  }
> >  
> >  /*
> > + * Returns a pool_id that is associated with a given fake poolid.
> 
> Was there a comment anywhere which tells the reader what a "fake poolid" is?
> 
> > + */
> > +static int get_poolid_from_fake(int fake_pool_id)
> > +{
> > +	if (fake_pool_id >= FAKE_SHARED_FS_POOLID_OFFSET)
> > +		return shared_fs_poolid_map[fake_pool_id -
> > +			FAKE_SHARED_FS_POOLID_OFFSET];
> > +	else if (fake_pool_id >= FAKE_FS_POOLID_OFFSET)
> > +		return fs_poolid_map[fake_pool_id - FAKE_FS_POOLID_OFFSET];
> > +	return FS_NO_BACKEND;
> > +}
> > +
> > +/*
> >   * "Get" data from cleancache associated with the poolid/inode/index
> >   * that were specified when the data was put to cleanache and, if
> >   * successful, use it to fill the specified page with data and return 0.
> > @@ -109,17 +175,26 @@ int __cleancache_get_page(struct page *page)
> >  {
> >  	int ret = -1;
> >  	int pool_id;
> > +	int fake_pool_id;
> >  	struct cleancache_filekey key = { .u.key = { 0 } };
> >  
> > +	if (!backend_registered) {
> > +		cleancache_failed_gets++;
> > +		goto out;
> > +	}
> 
> Races everywhere...
> 
> >  	VM_BUG_ON(!PageLocked(page));
> > -	pool_id = page->mapping->host->i_sb->cleancache_poolid;
> > -	if (pool_id < 0)
> > +	fake_pool_id = page->mapping->host->i_sb->cleancache_poolid;
> > +	if (fake_pool_id < 0)
> >  		goto out;
> > +	pool_id = get_poolid_from_fake(fake_pool_id);
> >  
> >  	if (cleancache_get_key(page->mapping->host, &key) < 0)
> >  		goto out;
> >  
> > -	ret = (*cleancache_ops.get_page)(pool_id, key, page->index, page);
> > +	if (pool_id >= 0)
> > +		ret = (*cleancache_ops.get_page)(pool_id,
> > +				key, page->index, page);
> >  	if (ret == 0)
> >  		cleancache_succ_gets++;
> >  	else
> > @@ -138,12 +213,23 @@ EXPORT_SYMBOL(__cleancache_get_page);
> >  void __cleancache_put_page(struct page *page)
> >  {
> >  	int pool_id;
> > +	int fake_pool_id;
> >  	struct cleancache_filekey key = { .u.key = { 0 } };
> >  
> > +	if (!backend_registered) {
> > +		cleancache_puts++;
> > +		return;
> > +	}
> 
> More..
> 
> >  	VM_BUG_ON(!PageLocked(page));
> > -	pool_id = page->mapping->host->i_sb->cleancache_poolid;
> > +	fake_pool_id = page->mapping->host->i_sb->cleancache_poolid;
> > +	if (fake_pool_id < 0)
> > +		return;
> > +
> > +	pool_id = get_poolid_from_fake(fake_pool_id);
> > +
> >  	if (pool_id >= 0 &&
> > -	      cleancache_get_key(page->mapping->host, &key) >= 0) {
> > +		cleancache_get_key(page->mapping->host, &key) >= 0) {
> >  		(*cleancache_ops.put_page)(pool_id, key, page->index, page);
> >  		cleancache_puts++;
> >  	}
> >
> > ...
> >
> 
> I don't understand the timing flow here, nor the existing constraints
> on what can be done and when, but....
> 
> The whole thing looks really hacky?  Why do we need to remember all
> this stuff for later on?  What prevents us from simply synchonously
> doing whatever we need to do when someone wants to register a backend?
> 
> Maybe a little ascii time chart/flow diagram would help.

This patch hopefully answers the questions and comments. It has a bit
of a a), then b), then c) type chart to illustrate the issue of backends
registered asynchronously.

>From aa306144b1be66cc3e53299a454e8fe2506e19c0 Mon Sep 17 00:00:00 2001
From: Dan Magenheimer <dan.magenheimer@...cle.com>
Date: Wed, 14 Nov 2012 13:57:05 -0500
Subject: [PATCH 1/8] mm: cleancache: lazy initialization to allow tmem
 backends to build/run as modules

With the goal of allowing tmem backends (zcache, ramster, Xen tmem) to be
built/loaded as modules rather than built-in and enabled by a boot parameter,
this patch provides "lazy initialization", allowing backends to register to
cleancache even after filesystems were mounted. Calls to init_fs and
init_shared_fs are remembered as fake poolids but no real tmem_pools created.
On backend registration the fake poolids are mapped to real poolids and
respective tmem_pools.

Signed-off-by: Stefan Hengelein <ilendir@...glemail.com>
Signed-off-by: Florian Schmaus <fschmaus@...il.com>
Signed-off-by: Andor Daam <andor.daam@...glemail.com>
Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
[v1: Minor fixes: used #define for some values and bools]
[v2: Removed CLEANCACHE_HAS_LAZY_INIT]
[v3: Added more comments, added a lock for [shared_|]fs_poolid_map]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
---
 mm/cleancache.c | 240 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 219 insertions(+), 21 deletions(-)

diff --git a/mm/cleancache.c b/mm/cleancache.c
index 32e6f41..e4dc314 100644
--- a/mm/cleancache.c
+++ b/mm/cleancache.c
@@ -45,15 +45,99 @@ static u64 cleancache_puts;
 static u64 cleancache_invalidates;
 
 /*
- * register operations for cleancache, returning previous thus allowing
- * detection of multiple backends and possible nesting
+ * When no backend is registered all calls to init_fs and init_shared_fs
+ * are registered and fake poolids (FAKE_FS_POOLID_OFFSET or
+ * FAKE_SHARED_FS_POOLID_OFFSET, plus offset in the respective array
+ * [shared_|]fs_poolid_map) are given to the respective super block
+ * (sb->cleancache_poolid) and no tmem_pools are created. When a backend
+ * registers with cleancache the previous calls to init_fs and init_shared_fs
+ * are executed to create tmem_pools and set the respective poolids. While no
+ * backend is registered all "puts", "gets" and "flushes" are ignored or failed.
+ */
+#define MAX_INITIALIZABLE_FS 32
+#define FAKE_FS_POOLID_OFFSET 1000
+#define FAKE_SHARED_FS_POOLID_OFFSET 2000
+
+#define FS_NO_BACKEND (-1)
+#define FS_UNKNOWN (-2)
+static int fs_poolid_map[MAX_INITIALIZABLE_FS];
+static int shared_fs_poolid_map[MAX_INITIALIZABLE_FS];
+static char *uuids[MAX_INITIALIZABLE_FS];
+/*
+ * Mutex for the [shared_|]fs_poolid_map to guard against multiple threads
+ * invoking umount (and ending in __cleancache_invalidate_fs) and also multiple
+ * threads calling mount (and ending up in __cleancache_init_[shared|]fs).
+ */
+static DEFINE_MUTEX(poolid_mutex);
+/*
+ * When set to false (default) all calls to the cleancache functions, except
+ * the __cleancache_invalidate_fs and __cleancache_init_[shared|]fs are guarded
+ * by the if (!backend_registered) return. This means multiple threads (from
+ * different filesystems) will be checking backend_registered. The usage of a
+ * bool instead of a atomic_t or a bool guarded by a spinlock is OK - we are
+ * OK if the time between the backend's have been initialized (and
+ * backend_registered has been set to true) and when the filesystems start
+ * actually calling the backends. The inverse (when unloading) is obviously
+ * not good - but this shim does not do that (yet).
+ */
+static bool backend_registered __read_mostly;
+
+/*
+ * The backends and filesystems work all asynchronously. This is b/c the
+ * backends can be built as modules.
+ * The usual sequence of events is:
+ * 	a) mount /	-> __cleancache_init_fs is called. We set the
+ * 		[shared_|]fs_poolid_map and uuids for.
+ *
+ * 	b). user does I/Os -> we call the rest of __cleancache_* functions
+ * 		which return immediately as backend_registered is false.
+ *
+ * 	c). modprobe zcache -> cleancache_register_ops. We init the backend
+ * 		and set backend_registered to true, and for any fs_poolid_map
+ * 		(which is set by __cleancache_init_fs) we initialize the poolid.
+ *
+ * 	d). user does I/Os -> now that backend_registered is true all the
+ * 		__cleancache_* functions can call the backend. They all check
+ * 		that fs_poolid_map is valid and if so invoke the backend.
+ *
+ * 	e). umount /	-> __cleancache_invalidate_fs, the fs_poolid_map is
+ * 		reset (which is the second check in the __cleancache_* ops
+ * 		to call the backend).
+ *
+ * The sequence of event could also be c), followed by a), and d). and e). The
+ * c) would not happen anymore. There is also the chance of c), and one thread
+ * doing a) + d), and another doing e). For that case we depend on the
+ * filesystem calling __cleancache_invalidate_fs in the proper sequence (so
+ * that it handles all I/Os before it invalidates the fs (which is last part
+ * of unmounting process).
+ *
+ * Note: The acute reader will notice that there is no "rmmod zcache" case.
+ * This is b/c the functionality for that is not yet implemented and when
+ * done, will require some extra locking not yet devised.
+ */
+
+/*
+ * Register operations for cleancache, returning previous thus allowing
+ * detection of multiple backends and possible nesting.
  */
 struct cleancache_ops cleancache_register_ops(struct cleancache_ops *ops)
 {
 	struct cleancache_ops old = cleancache_ops;
+	int i;
 
+	mutex_lock(&poolid_mutex);
 	cleancache_ops = *ops;
-	cleancache_enabled = 1;
+
+	backend_registered = true;
+	for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
+		if (fs_poolid_map[i] == FS_NO_BACKEND)
+			fs_poolid_map[i] = (*cleancache_ops.init_fs)(PAGE_SIZE);
+		if (shared_fs_poolid_map[i] == FS_NO_BACKEND)
+			shared_fs_poolid_map[i] = (*cleancache_ops.init_shared_fs)
+					(uuids[i], PAGE_SIZE);
+	}
+out:
+	mutex_unlock(&poolid_mutex);
 	return old;
 }
 EXPORT_SYMBOL(cleancache_register_ops);
@@ -61,15 +145,42 @@ EXPORT_SYMBOL(cleancache_register_ops);
 /* Called by a cleancache-enabled filesystem at time of mount */
 void __cleancache_init_fs(struct super_block *sb)
 {
-	sb->cleancache_poolid = (*cleancache_ops.init_fs)(PAGE_SIZE);
+	int i;
+
+	mutex_lock(&poolid_mutex);
+	for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
+		if (fs_poolid_map[i] == FS_UNKNOWN) {
+			sb->cleancache_poolid = i + FAKE_FS_POOLID_OFFSET;
+			if (backend_registered)
+				fs_poolid_map[i] = (*cleancache_ops.init_fs)(PAGE_SIZE);
+			else
+				fs_poolid_map[i] = FS_NO_BACKEND;
+			break;
+		}
+	}
+	mutex_unlock(&poolid_mutex);
 }
 EXPORT_SYMBOL(__cleancache_init_fs);
 
 /* Called by a cleancache-enabled clustered filesystem at time of mount */
 void __cleancache_init_shared_fs(char *uuid, struct super_block *sb)
 {
-	sb->cleancache_poolid =
-		(*cleancache_ops.init_shared_fs)(uuid, PAGE_SIZE);
+	int i;
+
+	mutex_lock(&poolid_mutex);
+	for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
+		if (shared_fs_poolid_map[i] == FS_UNKNOWN) {
+			sb->cleancache_poolid = i + FAKE_SHARED_FS_POOLID_OFFSET;
+			uuids[i] = uuid;
+			if (backend_registered)
+				shared_fs_poolid_map[i] = (*cleancache_ops.init_shared_fs)
+						(uuid, PAGE_SIZE);
+			else
+				shared_fs_poolid_map[i] = FS_NO_BACKEND;
+			break;
+		}
+	}
+	mutex_unlock(&poolid_mutex);
 }
 EXPORT_SYMBOL(__cleancache_init_shared_fs);
 
@@ -99,27 +210,53 @@ static int cleancache_get_key(struct inode *inode,
 }
 
 /*
+ * Returns a pool_id that is associated with a given fake poolid.
+ */
+static int get_poolid_from_fake(int fake_pool_id)
+{
+	if (fake_pool_id >= FAKE_SHARED_FS_POOLID_OFFSET)
+		return shared_fs_poolid_map[fake_pool_id -
+			FAKE_SHARED_FS_POOLID_OFFSET];
+	else if (fake_pool_id >= FAKE_FS_POOLID_OFFSET)
+		return fs_poolid_map[fake_pool_id - FAKE_FS_POOLID_OFFSET];
+	return FS_NO_BACKEND;
+}
+
+/*
  * "Get" data from cleancache associated with the poolid/inode/index
  * that were specified when the data was put to cleanache and, if
  * successful, use it to fill the specified page with data and return 0.
  * The pageframe is unchanged and returns -1 if the get fails.
  * Page must be locked by caller.
+ *
+ * The function has two checks before any action is taken - whether
+ * a backend is registered and whether the sb->cleancache_poolid
+ * is correct.
  */
 int __cleancache_get_page(struct page *page)
 {
 	int ret = -1;
 	int pool_id;
+	int fake_pool_id;
 	struct cleancache_filekey key = { .u.key = { 0 } };
 
+	if (!backend_registered) {
+		cleancache_failed_gets++;
+		goto out;
+	}
+
 	VM_BUG_ON(!PageLocked(page));
-	pool_id = page->mapping->host->i_sb->cleancache_poolid;
-	if (pool_id < 0)
+	fake_pool_id = page->mapping->host->i_sb->cleancache_poolid;
+	if (fake_pool_id < 0)
 		goto out;
+	pool_id = get_poolid_from_fake(fake_pool_id);
 
 	if (cleancache_get_key(page->mapping->host, &key) < 0)
 		goto out;
 
-	ret = (*cleancache_ops.get_page)(pool_id, key, page->index, page);
+	if (pool_id >= 0)
+		ret = (*cleancache_ops.get_page)(pool_id,
+				key, page->index, page);
 	if (ret == 0)
 		cleancache_succ_gets++;
 	else
@@ -134,16 +271,31 @@ EXPORT_SYMBOL(__cleancache_get_page);
  * (previously-obtained per-filesystem) poolid and the page's,
  * inode and page index.  Page must be locked.  Note that a put_page
  * always "succeeds", though a subsequent get_page may succeed or fail.
+ *
+ * The function has two checks before any action is taken - whether
+ * a backend is registered and whether the sb->cleancache_poolid
+ * is correct.
  */
 void __cleancache_put_page(struct page *page)
 {
 	int pool_id;
+	int fake_pool_id;
 	struct cleancache_filekey key = { .u.key = { 0 } };
 
+	if (!backend_registered) {
+		cleancache_puts++;
+		return;
+	}
+
 	VM_BUG_ON(!PageLocked(page));
-	pool_id = page->mapping->host->i_sb->cleancache_poolid;
+	fake_pool_id = page->mapping->host->i_sb->cleancache_poolid;
+	if (fake_pool_id < 0)
+		return;
+
+	pool_id = get_poolid_from_fake(fake_pool_id);
+
 	if (pool_id >= 0 &&
-	      cleancache_get_key(page->mapping->host, &key) >= 0) {
+		cleancache_get_key(page->mapping->host, &key) >= 0) {
 		(*cleancache_ops.put_page)(pool_id, key, page->index, page);
 		cleancache_puts++;
 	}
@@ -153,19 +305,31 @@ EXPORT_SYMBOL(__cleancache_put_page);
 /*
  * Invalidate any data from cleancache associated with the poolid and the
  * page's inode and page index so that a subsequent "get" will fail.
+ *
+ * The function has two checks before any action is taken - whether
+ * a backend is registered and whether the sb->cleancache_poolid
+ * is correct.
  */
 void __cleancache_invalidate_page(struct address_space *mapping,
 					struct page *page)
 {
 	/* careful... page->mapping is NULL sometimes when this is called */
-	int pool_id = mapping->host->i_sb->cleancache_poolid;
+	int pool_id;
+	int fake_pool_id = mapping->host->i_sb->cleancache_poolid;
 	struct cleancache_filekey key = { .u.key = { 0 } };
 
-	if (pool_id >= 0) {
+	if (!backend_registered)
+		return;
+
+	if (fake_pool_id >= 0) {
+		pool_id = get_poolid_from_fake(fake_pool_id);
+		if (pool_id < 0)
+			return;
+
 		VM_BUG_ON(!PageLocked(page));
 		if (cleancache_get_key(mapping->host, &key) >= 0) {
 			(*cleancache_ops.invalidate_page)(pool_id,
-							  key, page->index);
+					key, page->index);
 			cleancache_invalidates++;
 		}
 	}
@@ -176,12 +340,25 @@ EXPORT_SYMBOL(__cleancache_invalidate_page);
  * Invalidate all data from cleancache associated with the poolid and the
  * mappings's inode so that all subsequent gets to this poolid/inode
  * will fail.
+ *
+ * The function has two checks before any action is taken - whether
+ * a backend is registered and whether the sb->cleancache_poolid
+ * is correct.
  */
 void __cleancache_invalidate_inode(struct address_space *mapping)
 {
-	int pool_id = mapping->host->i_sb->cleancache_poolid;
+	int pool_id;
+	int fake_pool_id = mapping->host->i_sb->cleancache_poolid;
 	struct cleancache_filekey key = { .u.key = { 0 } };
 
+	if (!backend_registered)
+		return;
+
+	if (fake_pool_id < 0)
+		return;
+
+	pool_id = get_poolid_from_fake(fake_pool_id);
+
 	if (pool_id >= 0 && cleancache_get_key(mapping->host, &key) >= 0)
 		(*cleancache_ops.invalidate_inode)(pool_id, key);
 }
@@ -189,21 +366,37 @@ EXPORT_SYMBOL(__cleancache_invalidate_inode);
 
 /*
  * Called by any cleancache-enabled filesystem at time of unmount;
- * note that pool_id is surrendered and may be reutrned by a subsequent
- * cleancache_init_fs or cleancache_init_shared_fs
+ * note that pool_id is surrendered and may be returned by a subsequent
+ * cleancache_init_fs or cleancache_init_shared_fs.
  */
 void __cleancache_invalidate_fs(struct super_block *sb)
 {
-	if (sb->cleancache_poolid >= 0) {
-		int old_poolid = sb->cleancache_poolid;
-		sb->cleancache_poolid = -1;
-		(*cleancache_ops.invalidate_fs)(old_poolid);
+	int index;
+	int fake_pool_id = sb->cleancache_poolid;
+	int old_poolid = fake_pool_id;
+
+	mutex_lock(&poolid_mutex);
+	if (fake_pool_id >= FAKE_SHARED_FS_POOLID_OFFSET) {
+		index = fake_pool_id - FAKE_SHARED_FS_POOLID_OFFSET;
+		old_poolid = shared_fs_poolid_map[index];
+		shared_fs_poolid_map[index] = FS_UNKNOWN;
+		uuids[index] = NULL;
+	} else if (fake_pool_id >= FAKE_FS_POOLID_OFFSET) {
+		index = fake_pool_id - FAKE_FS_POOLID_OFFSET;
+		old_poolid = fs_poolid_map[index];
+		fs_poolid_map[index] = FS_UNKNOWN;
 	}
+	sb->cleancache_poolid = -1;
+	if (backend_registered)
+		(*cleancache_ops.invalidate_fs)(old_poolid);
+	mutex_unlock(&poolid_mutex);
 }
 EXPORT_SYMBOL(__cleancache_invalidate_fs);
 
 static int __init init_cleancache(void)
 {
+	int i;
+
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *root = debugfs_create_dir("cleancache", NULL);
 	if (root == NULL)
@@ -215,6 +408,11 @@ static int __init init_cleancache(void)
 	debugfs_create_u64("invalidates", S_IRUGO,
 				root, &cleancache_invalidates);
 #endif
+	for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
+		fs_poolid_map[i] = FS_UNKNOWN;
+		shared_fs_poolid_map[i] = FS_UNKNOWN;
+	}
+	cleancache_enabled = 1;
 	return 0;
 }
 module_init(init_cleancache)
-- 
1.7.11.7

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