Messages in this thread Patch in this message | | | Date | Thu, 15 Sep 2005 00:51:20 +1000 | From | Nick Piggin <> | Subject | [PATCH 3/5] rcu file: use atomic primitives |
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This removes rcuref.h in favour of using the new atomic primitives. Lightly tested on i386.
-- SUSE Labs, Novell Inc.
Index: linux-2.6/include/linux/rcuref.h =================================================================== --- linux-2.6.orig/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_ */ Index: linux-2.6/fs/aio.c =================================================================== --- linux-2.6.orig/fs/aio.c +++ linux-2.6/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> @@ -500,7 +499,7 @@ static int __aio_put_req(struct kioctx * /* 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); Index: linux-2.6/fs/file_table.c =================================================================== --- linux-2.6.orig/fs/file_table.c +++ linux-2.6/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 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(unsigne 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(unsigne 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); Index: linux-2.6/include/linux/fs.h =================================================================== --- linux-2.6.orig/include/linux/fs.h +++ linux-2.6/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 @@ -604,7 +603,7 @@ 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) Index: linux-2.6/Documentation/RCU/rcuref.txt =================================================================== --- linux-2.6.orig/Documentation/RCU/rcuref.txt +++ linux-2.6/Documentation/RCU/rcuref.txt @@ -31,9 +31,9 @@ release_referenced() delete() 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. @@ -41,7 +41,7 @@ add() search_and_reference() { { alloc_object rcu_read_lock(); ... search_for_element - atomic_set(&el->rc, 1); if (rcuref_inc_lf(&el->rc)) { + atomic_set(&el->rc, 1); if (atomic_inc_not_zero(&el->rc)) { write_lock(&list_lock); rcu_read_unlock(); return FAIL; add_element } @@ -52,23 +52,23 @@ add() search_and_reference() release_referenced() delete() { { ... write_lock(&list_lock); - rcuref_dec(&el->rc, relfunc) ... + atomic_dec(&el->rc, relfunc) ... ... delete_element } write_unlock(&list_lock); ... - if (rcuref_dec_and_test(&el->rc)) + 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 +For arches which do not have cmpxchg atomic_inc_not_zero 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 +is acquired in all atomic_xxx primitives to preserve atomicity. +Note: Use atomic_inc api only if you need to use atomic_inc_not_zero on the +refcounter atleast at one place. Mixing atomic_inc and atomic_xxx api +might lead to races. atomic_inc_not_zero() must be used in lockfree RCU critical sections only. | |