fs/locks: Replace lg_local with a per-cpu spinlock

As Oleg suggested, replace file_lock_list with a structure containing
the hlist head and a spinlock.

This completely removes the lglock from fs/locks.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Cc: der.herr@hofr.at
Cc: paulmck@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: tj@kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 30 insertions, 18 deletions

diff --git a/fs/Kconfig b/fs/Kconfig
index 2bc7ad775842..3ef62bad8f2b 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -79,6 +79,7 @@ config EXPORTFS_BLOCK_OPS
 config FILE_LOCKING
         bool "Enable POSIX file locking API" if EXPERT
         default y
+        select PERCPU_RWSEM
         help
           This option enables standard file locking support, required
           for filesystems like NFS and for the flock() system
diff --git a/fs/locks.c b/fs/locks.c
index 8f609ec03364..c33aa77fada2 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -127,7 +127,6 @@
 #include <linux/pid_namespace.h>
 #include <linux/hashtable.h>
 #include <linux/percpu.h>
-#include <linux/lglock.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/filelock.h>
@@ -158,12 +157,17 @@ int lease_break_time = 45;
 
 /*
  * The global file_lock_list is only used for displaying /proc/locks, so we
- * keep a list on each CPU, with each list protected by its own spinlock via
- * the file_lock_lglock. Note that alterations to the list also require that
- * the relevant flc_lock is held.
+ * keep a list on each CPU, with each list protected by its own spinlock.
+ * Global serialization is done using file_rwsem.
+ *
+ * Note that alterations to the list also require that the relevant flc_lock is
+ * held.
  */
-DEFINE_STATIC_LGLOCK(file_lock_lglock);
-static DEFINE_PER_CPU(struct hlist_head, file_lock_list);
+struct file_lock_list_struct {
+        spinlock_t              lock;
+        struct hlist_head       hlist;
+};
+static DEFINE_PER_CPU(struct file_lock_list_struct, file_lock_list);
 DEFINE_STATIC_PERCPU_RWSEM(file_rwsem);
 
 /*
@@ -588,17 +592,21 @@ static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)
 /* Must be called with the flc_lock held! */
 static void locks_insert_global_locks(struct file_lock *fl)
 {
+        struct file_lock_list_struct *fll = this_cpu_ptr(&file_lock_list);
+
         percpu_rwsem_assert_held(&file_rwsem);
 
-        lg_local_lock(&file_lock_lglock);
+        spin_lock(&fll->lock);
         fl->fl_link_cpu = smp_processor_id();
-        hlist_add_head(&fl->fl_link, this_cpu_ptr(&file_lock_list));
-        lg_local_unlock(&file_lock_lglock);
+        hlist_add_head(&fl->fl_link, &fll->hlist);
+        spin_unlock(&fll->lock);
 }
 
 /* Must be called with the flc_lock held! */
 static void locks_delete_global_locks(struct file_lock *fl)
 {
+        struct file_lock_list_struct *fll;
+
         percpu_rwsem_assert_held(&file_rwsem);
 
         /*
@@ -608,9 +616,11 @@ static void locks_delete_global_locks(struct file_lock *fl)
          */
         if (hlist_unhashed(&fl->fl_link))
                 return;
-        lg_local_lock_cpu(&file_lock_lglock, fl->fl_link_cpu);
+
+        fll = per_cpu_ptr(&file_lock_list, fl->fl_link_cpu);
+        spin_lock(&fll->lock);
         hlist_del_init(&fl->fl_link);
-        lg_local_unlock_cpu(&file_lock_lglock, fl->fl_link_cpu);
+        spin_unlock(&fll->lock);
 }
 
 static unsigned long
@@ -2723,9 +2733,8 @@ static void *locks_start(struct seq_file *f, loff_t *pos)
 
         iter->li_pos = *pos + 1;
         percpu_down_write(&file_rwsem);
-        lg_global_lock(&file_lock_lglock);
         spin_lock(&blocked_lock_lock);
-        return seq_hlist_start_percpu(&file_lock_list, &iter->li_cpu, *pos);
+        return seq_hlist_start_percpu(&file_lock_list.hlist, &iter->li_cpu, *pos);
 }
 
 static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
@@ -2733,14 +2742,13 @@ static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
         struct locks_iterator *iter = f->private;
 
         ++iter->li_pos;
-        return seq_hlist_next_percpu(v, &file_lock_list, &iter->li_cpu, pos);
+        return seq_hlist_next_percpu(v, &file_lock_list.hlist, &iter->li_cpu, pos);
 }
 
 static void locks_stop(struct seq_file *f, void *v)
         __releases(&blocked_lock_lock)
 {
         spin_unlock(&blocked_lock_lock);
-        lg_global_unlock(&file_lock_lglock);
         percpu_up_write(&file_rwsem);
 }
 
@@ -2782,10 +2790,13 @@ static int __init filelock_init(void)
         filelock_cache = kmem_cache_create("file_lock_cache",
                         sizeof(struct file_lock), 0, SLAB_PANIC, NULL);
 
-        lg_lock_init(&file_lock_lglock, "file_lock_lglock");
 
-        for_each_possible_cpu(i)
-                INIT_HLIST_HEAD(per_cpu_ptr(&file_lock_list, i));
+        for_each_possible_cpu(i) {
+                struct file_lock_list_struct *fll = per_cpu_ptr(&file_lock_list, i);
+
+                spin_lock_init(&fll->lock);
+                INIT_HLIST_HEAD(&fll->hlist);
+        }
 
         return 0;
 }