fs: move i_sb_list out from under inode_lock

Protect the per-sb inode list with a new global lock
inode_sb_list_lock and use it to protect the list manipulations and
traversals. This lock replaces the inode_lock as the inodes on the
list can be validity checked while holding the inode->i_lock and
hence the inode_lock is no longer needed to protect the list.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

6 files changed, 67 insertions, 56 deletions

diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index 6c6f73ba0868..98b77c89494c 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -8,6 +8,7 @@
 #include <linux/writeback.h>
 #include <linux/sysctl.h>
 #include <linux/gfp.h>
+#include "internal.h"
 
 /* A global variable is a bit ugly, but it keeps the code simple */
 int sysctl_drop_caches;
@@ -16,7 +17,7 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
 {
         struct inode *inode, *toput_inode = NULL;
 
-        spin_lock(&inode_lock);
+        spin_lock(&inode_sb_list_lock);
         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
                 spin_lock(&inode->i_lock);
                 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
@@ -26,13 +27,13 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
                 }
                 __iget(inode);
                 spin_unlock(&inode->i_lock);
-                spin_unlock(&inode_lock);
+                spin_unlock(&inode_sb_list_lock);
                 invalidate_mapping_pages(inode->i_mapping, 0, -1);
                 iput(toput_inode);
                 toput_inode = inode;
-                spin_lock(&inode_lock);
+                spin_lock(&inode_sb_list_lock);
         }
-        spin_unlock(&inode_lock);
+        spin_unlock(&inode_sb_list_lock);
         iput(toput_inode);
 }
 
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index efd1ebe879cc..5de56a2182bb 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1123,7 +1123,7 @@ static void wait_sb_inodes(struct super_block *sb)
          */
         WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-        spin_lock(&inode_lock);
+        spin_lock(&inode_sb_list_lock);
 
         /*
          * Data integrity sync. Must wait for all pages under writeback,
@@ -1143,14 +1143,15 @@ static void wait_sb_inodes(struct super_block *sb)
                 }
                 __iget(inode);
                 spin_unlock(&inode->i_lock);
-                spin_unlock(&inode_lock);
+                spin_unlock(&inode_sb_list_lock);
+
                 /*
-                 * We hold a reference to 'inode' so it couldn't have
-                 * been removed from s_inodes list while we dropped the
-                 * inode_lock.  We cannot iput the inode now as we can
-                 * be holding the last reference and we cannot iput it
-                 * under inode_lock. So we keep the reference and iput
-                 * it later.
+                 * We hold a reference to 'inode' so it couldn't have been
+                 * removed from s_inodes list while we dropped the
+                 * inode_sb_list_lock.  We cannot iput the inode now as we can
+                 * be holding the last reference and we cannot iput it under
+                 * inode_sb_list_lock. So we keep the reference and iput it
+                 * later.
                  */
                 iput(old_inode);
                 old_inode = inode;
@@ -1159,9 +1160,9 @@ static void wait_sb_inodes(struct super_block *sb)
 
                 cond_resched();
 
-                spin_lock(&inode_lock);
+                spin_lock(&inode_sb_list_lock);
         }
-        spin_unlock(&inode_lock);
+        spin_unlock(&inode_sb_list_lock);
         iput(old_inode);
 }
 
diff --git a/fs/inode.c b/fs/inode.c
index 389f5a247599..785b1ab23ff0 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -34,10 +34,15 @@
  *   inode->i_state, inode->i_hash, __iget()
  * inode_lru_lock protects:
  *   inode_lru, inode->i_lru
+ * inode_sb_list_lock protects:
+ *   sb->s_inodes, inode->i_sb_list
  *
  * Lock ordering:
  * inode_lock
  *   inode->i_lock
+ *
+ * inode_sb_list_lock
+ *   inode->i_lock
  *     inode_lru_lock
  */
 
@@ -99,6 +104,8 @@ static struct hlist_head *inode_hashtable __read_mostly;
  */
 DEFINE_SPINLOCK(inode_lock);
 
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_sb_list_lock);
+
 /*
  * iprune_sem provides exclusion between the icache shrinking and the
  * umount path.
@@ -378,26 +385,23 @@ static void inode_lru_list_del(struct inode *inode)
         spin_unlock(&inode_lru_lock);
 }
 
-static inline void __inode_sb_list_add(struct inode *inode)
-{
-        list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
-}
-
 /**
  * inode_sb_list_add - add inode to the superblock list of inodes
  * @inode: inode to add
  */
 void inode_sb_list_add(struct inode *inode)
 {
-        spin_lock(&inode_lock);
-        __inode_sb_list_add(inode);
-        spin_unlock(&inode_lock);
+        spin_lock(&inode_sb_list_lock);
+        list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
+        spin_unlock(&inode_sb_list_lock);
 }
 EXPORT_SYMBOL_GPL(inode_sb_list_add);
 
-static inline void __inode_sb_list_del(struct inode *inode)
+static inline void inode_sb_list_del(struct inode *inode)
 {
+        spin_lock(&inode_sb_list_lock);
         list_del_init(&inode->i_sb_list);
+        spin_unlock(&inode_sb_list_lock);
 }
 
 static unsigned long hash(struct super_block *sb, unsigned long hashval)
@@ -481,9 +485,10 @@ static void evict(struct inode *inode)
 
         spin_lock(&inode_lock);
         list_del_init(&inode->i_wb_list);
-        __inode_sb_list_del(inode);
         spin_unlock(&inode_lock);
 
+        inode_sb_list_del(inode);
+
         if (op->evict_inode) {
                 op->evict_inode(inode);
         } else {
@@ -539,7 +544,7 @@ void evict_inodes(struct super_block *sb)
         struct inode *inode, *next;
         LIST_HEAD(dispose);
 
-        spin_lock(&inode_lock);
+        spin_lock(&inode_sb_list_lock);
         list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
                 if (atomic_read(&inode->i_count))
                         continue;
@@ -555,7 +560,7 @@ void evict_inodes(struct super_block *sb)
                 spin_unlock(&inode->i_lock);
                 list_add(&inode->i_lru, &dispose);
         }
-        spin_unlock(&inode_lock);
+        spin_unlock(&inode_sb_list_lock);
 
         dispose_list(&dispose);
 
@@ -584,7 +589,7 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
         struct inode *inode, *next;
         LIST_HEAD(dispose);
 
-        spin_lock(&inode_lock);
+        spin_lock(&inode_sb_list_lock);
         list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
                 spin_lock(&inode->i_lock);
                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
@@ -607,7 +612,7 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
                 spin_unlock(&inode->i_lock);
                 list_add(&inode->i_lru, &dispose);
         }
-        spin_unlock(&inode_lock);
+        spin_unlock(&inode_sb_list_lock);
 
         dispose_list(&dispose);
 
@@ -867,16 +872,14 @@ struct inode *new_inode(struct super_block *sb)
 {
         struct inode *inode;
 
-        spin_lock_prefetch(&inode_lock);
+        spin_lock_prefetch(&inode_sb_list_lock);
 
         inode = alloc_inode(sb);
         if (inode) {
-                spin_lock(&inode_lock);
                 spin_lock(&inode->i_lock);
                 inode->i_state = 0;
                 spin_unlock(&inode->i_lock);
-                __inode_sb_list_add(inode);
-                spin_unlock(&inode_lock);
+                inode_sb_list_add(inode);
         }
         return inode;
 }
@@ -945,7 +948,7 @@ static struct inode *get_new_inode(struct super_block *sb,
                         inode->i_state = I_NEW;
                         hlist_add_head(&inode->i_hash, head);
                         spin_unlock(&inode->i_lock);
-                        __inode_sb_list_add(inode);
+                        inode_sb_list_add(inode);
                         spin_unlock(&inode_lock);
 
                         /* Return the locked inode with I_NEW set, the
@@ -994,7 +997,7 @@ static struct inode *get_new_inode_fast(struct super_block *sb,
                         inode->i_state = I_NEW;
                         hlist_add_head(&inode->i_hash, head);
                         spin_unlock(&inode->i_lock);
-                        __inode_sb_list_add(inode);
+                        inode_sb_list_add(inode);
                         spin_unlock(&inode_lock);
 
                         /* Return the locked inode with I_NEW set, the
diff --git a/fs/internal.h b/fs/internal.h
index 8318059b42c6..7013ae0c88c1 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -125,6 +125,8 @@ extern long do_handle_open(int mountdirfd,
 /*
  * inode.c
  */
+extern spinlock_t inode_sb_list_lock;
+
 extern int get_nr_dirty_inodes(void);
 extern void evict_inodes(struct super_block *);
 extern int invalidate_inodes(struct super_block *, bool);
diff --git a/fs/notify/inode_mark.c b/fs/notify/inode_mark.c
index 4dd53fb44124..fb3b3c5ef0ee 100644
--- a/fs/notify/inode_mark.c
+++ b/fs/notify/inode_mark.c
@@ -29,6 +29,8 @@
 #include <linux/fsnotify_backend.h>
 #include "fsnotify.h"
 
+#include "../internal.h"
+
 /*
  * Recalculate the mask of events relevant to a given inode locked.
  */
@@ -237,15 +239,14 @@ out:
  * fsnotify_unmount_inodes - an sb is unmounting.  handle any watched inodes.
  * @list: list of inodes being unmounted (sb->s_inodes)
  *
- * Called with inode_lock held, protecting the unmounting super block's list
- * of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay.
- * We temporarily drop inode_lock, however, and CAN block.
+ * Called during unmount with no locks held, so needs to be safe against
+ * concurrent modifiers. We temporarily drop inode_sb_list_lock and CAN block.
  */
 void fsnotify_unmount_inodes(struct list_head *list)
 {
         struct inode *inode, *next_i, *need_iput = NULL;
 
-        spin_lock(&inode_lock);
+        spin_lock(&inode_sb_list_lock);
         list_for_each_entry_safe(inode, next_i, list, i_sb_list) {
                 struct inode *need_iput_tmp;
 
@@ -293,12 +294,11 @@ void fsnotify_unmount_inodes(struct list_head *list)
                 }
 
                 /*
-                 * We can safely drop inode_lock here because we hold
+                 * We can safely drop inode_sb_list_lock here because we hold
                  * references on both inode and next_i.  Also no new inodes
-                 * will be added since the umount has begun.  Finally,
-                 * iprune_mutex keeps shrink_icache_memory() away.
+                 * will be added since the umount has begun.
                  */
-                spin_unlock(&inode_lock);
+                spin_unlock(&inode_sb_list_lock);
 
                 if (need_iput_tmp)
                         iput(need_iput_tmp);
@@ -310,7 +310,7 @@ void fsnotify_unmount_inodes(struct list_head *list)
 
                 iput(inode);
 
-                spin_lock(&inode_lock);
+                spin_lock(&inode_sb_list_lock);
         }
-        spin_unlock(&inode_lock);
+        spin_unlock(&inode_sb_list_lock);
 }
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index a1470fda366c..fcc8ae75d874 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -76,7 +76,7 @@
 #include <linux/buffer_head.h>
 #include <linux/capability.h>
 #include <linux/quotaops.h>
-#include <linux/writeback.h> /* for inode_lock, oddly enough.. */
+#include "../internal.h" /* ugh */
 
 #include <asm/uaccess.h>
 
@@ -900,7 +900,7 @@ static void add_dquot_ref(struct super_block *sb, int type)
         int reserved = 0;
 #endif
 
-        spin_lock(&inode_lock);
+        spin_lock(&inode_sb_list_lock);
         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
                 spin_lock(&inode->i_lock);
                 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
@@ -915,19 +915,23 @@ static void add_dquot_ref(struct super_block *sb, int type)
 #endif
                 __iget(inode);
                 spin_unlock(&inode->i_lock);
-                spin_unlock(&inode_lock);
+                spin_unlock(&inode_sb_list_lock);
 
                 iput(old_inode);
                 __dquot_initialize(inode, type);
-                /* We hold a reference to 'inode' so it couldn't have been
-                 * removed from s_inodes list while we dropped the inode_lock.
-                 * We cannot iput the inode now as we can be holding the last
-                 * reference and we cannot iput it under inode_lock. So we
-                 * keep the reference and iput it later. */
+
+                /*
+                 * We hold a reference to 'inode' so it couldn't have been
+                 * removed from s_inodes list while we dropped the
+                 * inode_sb_list_lock We cannot iput the inode now as we can be
+                 * holding the last reference and we cannot iput it under
+                 * inode_sb_list_lock. So we keep the reference and iput it
+                 * later.
+                 */
                 old_inode = inode;
-                spin_lock(&inode_lock);
+                spin_lock(&inode_sb_list_lock);
         }
-        spin_unlock(&inode_lock);
+        spin_unlock(&inode_sb_list_lock);
         iput(old_inode);
 
 #ifdef CONFIG_QUOTA_DEBUG
@@ -1008,7 +1012,7 @@ static void remove_dquot_ref(struct super_block *sb, int type,
         struct inode *inode;
         int reserved = 0;
 
-        spin_lock(&inode_lock);
+        spin_lock(&inode_sb_list_lock);
         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
                 /*
                  *  We have to scan also I_NEW inodes because they can already
@@ -1022,7 +1026,7 @@ static void remove_dquot_ref(struct super_block *sb, int type,
                         remove_inode_dquot_ref(inode, type, tofree_head);
                 }
         }
-        spin_unlock(&inode_lock);
+        spin_unlock(&inode_sb_list_lock);
 #ifdef CONFIG_QUOTA_DEBUG
         if (reserved) {
                 printk(KERN_WARNING "VFS (%s): Writes happened after quota"