[PATCH] rcu file: use atomic primitives

Use atomic_inc_not_zero for rcu files instead of special case rcuref.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

9 files changed, 48 insertions, 291 deletions

diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index a23fee66064d..3f60db41b2f0 100644
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -1,74 +1,67 @@
-Refcounter framework for elements of lists/arrays protected by
-RCU.
+Refcounter design for elements of lists/arrays protected by RCU.
 
 Refcounting on elements of  lists which are protected by traditional
 reader/writer spinlocks or semaphores are straight forward as in:
 
-1.                                      2.
-add()                                   search_and_reference()
-{                                       {
-        alloc_object                            read_lock(&list_lock);
-        ...                                     search_for_element
-        atomic_set(&el->rc, 1);                 atomic_inc(&el->rc);
-        write_lock(&list_lock);                 ...
-        add_element                             read_unlock(&list_lock);
-        ...                                     ...
-        write_unlock(&list_lock);       }
+1.                              2.
+add()                           search_and_reference()
+{                               {
+    alloc_object                    read_lock(&list_lock);
+    ...                             search_for_element
+    atomic_set(&el->rc, 1);         atomic_inc(&el->rc);
+    write_lock(&list_lock);          ...
+    add_element                     read_unlock(&list_lock);
+    ...                             ...
+    write_unlock(&list_lock);   }
 }
 
 3.                                      4.
 release_referenced()                    delete()
 {                                       {
-        ...                             write_lock(&list_lock);
-        atomic_dec(&el->rc, relfunc)    ...
-        ...                             delete_element
-}                                       write_unlock(&list_lock);
-                                        ...
-                                        if (atomic_dec_and_test(&el->rc))
-                                                kfree(el);
-                                        ...
+    ...                                     write_lock(&list_lock);
+    atomic_dec(&el->rc, relfunc)            ...
+    ...                                     delete_element
+}                                           write_unlock(&list_lock);
+                                            ...
+                                            if (atomic_dec_and_test(&el->rc))
+                                                kfree(el);
+                                            ...
                                         }
 
 If this list/array is made lock free using rcu as in changing the
 write_lock in add() and delete() to spin_lock and changing read_lock
-in search_and_reference to rcu_read_lock(), the rcuref_get in
+in search_and_reference to rcu_read_lock(), the atomic_get in
 search_and_reference could potentially hold reference to an element which
-has already been deleted from the list/array.  rcuref_lf_get_rcu takes
+has already been deleted from the list/array.  atomic_inc_not_zero takes
 care of this scenario. search_and_reference should look as;
 
 1.                                      2.
 add()                                   search_and_reference()
 {                                       {
-        alloc_object                            rcu_read_lock();
-        ...                                     search_for_element
-        atomic_set(&el->rc, 1);                 if (rcuref_inc_lf(&el->rc)) {
-        write_lock(&list_lock);                         rcu_read_unlock();
-                                                        return FAIL;
-        add_element                             }
-        ...                                     ...
-        write_unlock(&list_lock);               rcu_read_unlock();
+    alloc_object                            rcu_read_lock();
+    ...                                     search_for_element
+    atomic_set(&el->rc, 1);                 if (atomic_inc_not_zero(&el->rc)) {
+    write_lock(&list_lock);                     rcu_read_unlock();
+                                                return FAIL;
+    add_element                             }
+    ...                                     ...
+    write_unlock(&list_lock);               rcu_read_unlock();
 }                                       }
 3.                                      4.
 release_referenced()                    delete()
 {                                       {
-        ...                             write_lock(&list_lock);
-        rcuref_dec(&el->rc, relfunc)    ...
-        ...                             delete_element
-}                                       write_unlock(&list_lock);
-                                        ...
-                                        if (rcuref_dec_and_test(&el->rc))
-                                                call_rcu(&el->head, el_free);
-                                        ...
+    ...                                     write_lock(&list_lock);
+    atomic_dec(&el->rc, relfunc)            ...
+    ...                                     delete_element
+}                                           write_unlock(&list_lock);
+                                            ...
+                                            if (atomic_dec_and_test(&el->rc))
+                                                call_rcu(&el->head, el_free);
+                                            ...
                                         }
 
 Sometimes, reference to the element need to be obtained in the
-update (write) stream.  In such cases, rcuref_inc_lf might be an overkill
-since the spinlock serialising list updates are held. rcuref_inc
+update (write) stream.  In such cases, atomic_inc_not_zero might be an
+overkill since the spinlock serialising list updates are held. atomic_inc
 is to be used in such cases.
-For arches which do not have cmpxchg rcuref_inc_lf
-api uses a hashed spinlock implementation and the same hashed spinlock
-is acquired in all rcuref_xxx primitives to preserve atomicity.
-Note: Use rcuref_inc api only if you need to use rcuref_inc_lf on the
-refcounter atleast at one place.  Mixing rcuref_inc and atomic_xxx api
-might lead to races. rcuref_inc_lf() must be used in lockfree
-RCU critical sections only.
+
diff --git a/fs/aio.c b/fs/aio.c
index 5a28b69ad223..aec2b1916d1b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -29,7 +29,6 @@
 #include <linux/highmem.h>
 #include <linux/workqueue.h>
 #include <linux/security.h>
-#include <linux/rcuref.h>
 
 #include <asm/kmap_types.h>
 #include <asm/uaccess.h>
@@ -514,7 +513,7 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
         /* Must be done under the lock to serialise against cancellation.
          * Call this aio_fput as it duplicates fput via the fput_work.
          */
-        if (unlikely(rcuref_dec_and_test(&req->ki_filp->f_count))) {
+        if (unlikely(atomic_dec_and_test(&req->ki_filp->f_count))) {
                 get_ioctx(ctx);
                 spin_lock(&fput_lock);
                 list_add(&req->ki_list, &fput_head);
diff --git a/fs/file_table.c b/fs/file_table.c
index c3a5e2fd663b..6142250104a6 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -117,7 +117,7 @@ EXPORT_SYMBOL(get_empty_filp);
 
 void fastcall fput(struct file *file)
 {
-        if (rcuref_dec_and_test(&file->f_count))
+        if (atomic_dec_and_test(&file->f_count))
                 __fput(file);
 }
 
@@ -166,7 +166,7 @@ struct file fastcall *fget(unsigned int fd)
         rcu_read_lock();
         file = fcheck_files(files, fd);
         if (file) {
-                if (!rcuref_inc_lf(&file->f_count)) {
+                if (!atomic_inc_not_zero(&file->f_count)) {
                         /* File object ref couldn't be taken */
                         rcu_read_unlock();
                         return NULL;
@@ -198,7 +198,7 @@ struct file fastcall *fget_light(unsigned int fd, int *fput_needed)
                 rcu_read_lock();
                 file = fcheck_files(files, fd);
                 if (file) {
-                        if (rcuref_inc_lf(&file->f_count))
+                        if (atomic_inc_not_zero(&file->f_count))
                                 *fput_needed = 1;
                         else
                                 /* Didn't get the reference, someone's freed */
@@ -213,7 +213,7 @@ struct file fastcall *fget_light(unsigned int fd, int *fput_needed)
 
 void put_filp(struct file *file)
 {
-        if (rcuref_dec_and_test(&file->f_count)) {
+        if (atomic_dec_and_test(&file->f_count)) {
                 security_file_free(file);
                 file_kill(file);
                 file_free(file);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2c9c48d65630..ef29500b5df8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -9,7 +9,6 @@
 #include <linux/config.h>
 #include <linux/limits.h>
 #include <linux/ioctl.h>
-#include <linux/rcuref.h>
 
 /*
  * It's silly to have NR_OPEN bigger than NR_FILE, but you can change
@@ -653,7 +652,7 @@ extern spinlock_t files_lock;
 #define file_list_lock() spin_lock(&files_lock);
 #define file_list_unlock() spin_unlock(&files_lock);
 
-#define get_file(x)     rcuref_inc(&(x)->f_count)
+#define get_file(x)     atomic_inc(&(x)->f_count)
 #define file_count(x)   atomic_read(&(x)->f_count)
 
 #define MAX_NON_LFS     ((1UL<<31) - 1)
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 36e5d269612f..c57ff2fcb30a 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -19,6 +19,7 @@
 #ifndef _LINUX_RADIX_TREE_H
 #define _LINUX_RADIX_TREE_H
 
+#include <linux/sched.h>
 #include <linux/preempt.h>
 #include <linux/types.h>
 
diff --git a/include/linux/rcuref.h b/include/linux/rcuref.h
deleted file mode 100644
index e1adbba14b67..000000000000
--- a/include/linux/rcuref.h
+++ /dev/null
@@ -1,220 +0,0 @@
-/*
- * rcuref.h
- *
- * Reference counting for elements of lists/arrays protected by
- * RCU.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- *
- * Copyright (C) IBM Corporation, 2005
- *
- * Author: Dipankar Sarma <dipankar@in.ibm.com>
- *         Ravikiran Thirumalai <kiran_th@gmail.com>
- *
- * See Documentation/RCU/rcuref.txt for detailed user guide.
- *
- */
-
-#ifndef _RCUREF_H_
-#define _RCUREF_H_
-
-#ifdef __KERNEL__
-
-#include <linux/types.h>
-#include <linux/interrupt.h>
-#include <linux/spinlock.h>
-#include <asm/atomic.h>
-
-/*
- * These APIs work on traditional atomic_t counters used in the
- * kernel for reference counting. Under special circumstances
- * where a lock-free get() operation races with a put() operation
- * these APIs can be used. See Documentation/RCU/rcuref.txt.
- */
-
-#ifdef __HAVE_ARCH_CMPXCHG
-
-/**
- * rcuref_inc - increment refcount for object.
- * @rcuref: reference counter in the object in question.
- *
- * This should be used only for objects where we use RCU and
- * use the rcuref_inc_lf() api to acquire a reference
- * in a lock-free reader-side critical section.
- */
-static inline void rcuref_inc(atomic_t *rcuref)
-{
-        atomic_inc(rcuref);
-}
-
-/**
- * rcuref_dec - decrement refcount for object.
- * @rcuref: reference counter in the object in question.
- *
- * This should be used only for objects where we use RCU and
- * use the rcuref_inc_lf() api to acquire a reference
- * in a lock-free reader-side critical section.
- */
-static inline void rcuref_dec(atomic_t *rcuref)
-{
-        atomic_dec(rcuref);
-}
-
-/**
- * rcuref_dec_and_test - decrement refcount for object and test
- * @rcuref: reference counter in the object.
- * @release: pointer to the function that will clean up the object
- *           when the last reference to the object is released.
- *           This pointer is required.
- *
- * Decrement the refcount, and if 0, return 1. Else return 0.
- *
- * This should be used only for objects where we use RCU and
- * use the rcuref_inc_lf() api to acquire a reference
- * in a lock-free reader-side critical section.
- */
-static inline int rcuref_dec_and_test(atomic_t *rcuref)
-{
-        return atomic_dec_and_test(rcuref);
-}
-
-/*
- * cmpxchg is needed on UP too, if deletions to the list/array can happen
- * in interrupt context.
- */
-
-/**
- * rcuref_inc_lf - Take reference to an object in a read-side
- * critical section protected by RCU.
- * @rcuref: reference counter in the object in question.
- *
- * Try and increment the refcount by 1.  The increment might fail if
- * the reference counter has been through a 1 to 0 transition and
- * is no longer part of the lock-free list.
- * Returns non-zero on successful increment and zero otherwise.
- */
-static inline int rcuref_inc_lf(atomic_t *rcuref)
-{
-        int c, old;
-        c = atomic_read(rcuref);
-        while (c && (old = cmpxchg(&rcuref->counter, c, c + 1)) != c)
-                c = old;
-        return c;
-}
-
-#else                           /* !__HAVE_ARCH_CMPXCHG */
-
-extern spinlock_t __rcuref_hash[];
-
-/*
- * Use a hash table of locks to protect the reference count
- * since cmpxchg is not available in this arch.
- */
-#ifdef  CONFIG_SMP
-#define RCUREF_HASH_SIZE        4
-#define RCUREF_HASH(k) \
-        (&__rcuref_hash[(((unsigned long)k)>>8) & (RCUREF_HASH_SIZE-1)])
-#else
-#define RCUREF_HASH_SIZE        1
-#define RCUREF_HASH(k)  &__rcuref_hash[0]
-#endif                          /* CONFIG_SMP */
-
-/**
- * rcuref_inc - increment refcount for object.
- * @rcuref: reference counter in the object in question.
- *
- * This should be used only for objects where we use RCU and
- * use the rcuref_inc_lf() api to acquire a reference in a lock-free
- * reader-side critical section.
- */
-static inline void rcuref_inc(atomic_t *rcuref)
-{
-        unsigned long flags;
-        spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
-        rcuref->counter += 1;
-        spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
-}
-
-/**
- * rcuref_dec - decrement refcount for object.
- * @rcuref: reference counter in the object in question.
- *
- * This should be used only for objects where we use RCU and
- * use the rcuref_inc_lf() api to acquire a reference in a lock-free
- * reader-side critical section.
- */
-static inline void rcuref_dec(atomic_t *rcuref)
-{
-        unsigned long flags;
-        spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
-        rcuref->counter -= 1;
-        spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
-}
-
-/**
- * rcuref_dec_and_test - decrement refcount for object and test
- * @rcuref: reference counter in the object.
- * @release: pointer to the function that will clean up the object
- *           when the last reference to the object is released.
- *           This pointer is required.
- *
- * Decrement the refcount, and if 0, return 1. Else return 0.
- *
- * This should be used only for objects where we use RCU and
- * use the rcuref_inc_lf() api to acquire a reference in a lock-free
- * reader-side critical section.
- */
-static inline int rcuref_dec_and_test(atomic_t *rcuref)
-{
-        unsigned long flags;
-        spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
-        rcuref->counter--;
-        if (!rcuref->counter) {
-                spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
-                return 1;
-        } else {
-                spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
-                return 0;
-        }
-}
-
-/**
- * rcuref_inc_lf - Take reference to an object of a lock-free collection
- * by traversing a lock-free list/array.
- * @rcuref: reference counter in the object in question.
- *
- * Try and increment the refcount by 1.  The increment might fail if
- * the reference counter has been through a 1 to 0 transition and
- * object is no longer part of the lock-free list.
- * Returns non-zero on successful increment and zero otherwise.
- */
-static inline int rcuref_inc_lf(atomic_t *rcuref)
-{
-        int ret;
-        unsigned long flags;
-        spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
-        if (rcuref->counter)
-                ret = rcuref->counter++;
-        else
-                ret = 0;
-        spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
-        return ret;
-}
-
-
-#endif /* !__HAVE_ARCH_CMPXCHG */
-
-#endif /* __KERNEL__ */
-#endif /* _RCUREF_H_ */
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 0a669bd2f6d1..30b0bba03859 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -46,7 +46,6 @@
 #include <linux/percpu.h>
 #include <linux/notifier.h>
 #include <linux/rcupdate.h>
-#include <linux/rcuref.h>
 #include <linux/cpu.h>
 
 /* Definition for rcupdate control block. */
@@ -74,19 +73,6 @@ DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
 static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
 static int maxbatch = 10000;
 
-#ifndef __HAVE_ARCH_CMPXCHG
-/*
- * We use an array of spinlocks for the rcurefs -- similar to ones in sparc
- * 32 bit atomic_t implementations, and a hash function similar to that
- * for our refcounting needs.
- * Can't help multiprocessors which donot have cmpxchg :(
- */
-
-spinlock_t __rcuref_hash[RCUREF_HASH_SIZE] = {
-        [0 ... (RCUREF_HASH_SIZE-1)] = SPIN_LOCK_UNLOCKED
-};
-#endif
-
 /**
  * call_rcu - Queue an RCU callback for invocation after a grace period.
  * @head: structure to be used for queueing the RCU updates.
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 36efe088ad81..75174c81529a 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -39,7 +39,6 @@
 #include <linux/moduleparam.h>
 #include <linux/percpu.h>
 #include <linux/notifier.h>
-#include <linux/rcuref.h>
 #include <linux/cpu.h>
 #include <linux/random.h>
 #include <linux/delay.h>
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 3d496eae1b47..6647204e4636 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1663,7 +1663,7 @@ static inline void flush_unauthorized_files(struct files_struct * files)
                                                 continue;
                                         }
                                         if (devnull) {
-                                                rcuref_inc(&devnull->f_count);
+                                                get_file(devnull);
                                         } else {
                                                 devnull = dentry_open(dget(selinux_null), mntget(selinuxfs_mount), O_RDWR);
                                                 if (!devnull) {