6aa7de0591
Please do not apply this to mainline directly, instead please re-run the
coccinelle script shown below and apply its output.
For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't harmful, and changing them results in
churn.
However, for some features, the read/write distinction is critical to
correct operation. To distinguish these cases, separate read/write
accessors must be used. This patch migrates (most) remaining
ACCESS_ONCE() instances to {READ,WRITE}_ONCE(), using the following
coccinelle script:
----
// Convert trivial ACCESS_ONCE() uses to equivalent READ_ONCE() and
// WRITE_ONCE()
// $ make coccicheck COCCI=/home/mark/once.cocci SPFLAGS="--include-headers" MODE=patch
virtual patch
@ depends on patch @
expression E1, E2;
@@
- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)
@ depends on patch @
expression E;
@@
- ACCESS_ONCE(E)
+ READ_ONCE(E)
----
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-19-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
104 lines
3.1 KiB
C
104 lines
3.1 KiB
C
/*
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* Lock-less NULL terminated single linked list
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*
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* The basic atomic operation of this list is cmpxchg on long. On
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* architectures that don't have NMI-safe cmpxchg implementation, the
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* list can NOT be used in NMI handlers. So code that uses the list in
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* an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
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*
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* Copyright 2010,2011 Intel Corp.
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* Author: Huang Ying <ying.huang@intel.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License version
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* 2 as published by the Free Software Foundation;
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/llist.h>
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/**
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* llist_add_batch - add several linked entries in batch
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* @new_first: first entry in batch to be added
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* @new_last: last entry in batch to be added
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* @head: the head for your lock-less list
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*
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* Return whether list is empty before adding.
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*/
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bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
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struct llist_head *head)
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{
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struct llist_node *first;
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do {
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new_last->next = first = READ_ONCE(head->first);
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} while (cmpxchg(&head->first, first, new_first) != first);
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return !first;
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}
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EXPORT_SYMBOL_GPL(llist_add_batch);
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/**
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* llist_del_first - delete the first entry of lock-less list
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* @head: the head for your lock-less list
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*
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* If list is empty, return NULL, otherwise, return the first entry
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* deleted, this is the newest added one.
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*
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* Only one llist_del_first user can be used simultaneously with
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* multiple llist_add users without lock. Because otherwise
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* llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
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* llist_add) sequence in another user may change @head->first->next,
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* but keep @head->first. If multiple consumers are needed, please
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* use llist_del_all or use lock between consumers.
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*/
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struct llist_node *llist_del_first(struct llist_head *head)
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{
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struct llist_node *entry, *old_entry, *next;
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entry = smp_load_acquire(&head->first);
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for (;;) {
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if (entry == NULL)
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return NULL;
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old_entry = entry;
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next = READ_ONCE(entry->next);
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entry = cmpxchg(&head->first, old_entry, next);
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if (entry == old_entry)
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break;
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}
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return entry;
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}
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EXPORT_SYMBOL_GPL(llist_del_first);
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/**
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* llist_reverse_order - reverse order of a llist chain
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* @head: first item of the list to be reversed
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*
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* Reverse the order of a chain of llist entries and return the
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* new first entry.
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*/
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struct llist_node *llist_reverse_order(struct llist_node *head)
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{
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struct llist_node *new_head = NULL;
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while (head) {
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struct llist_node *tmp = head;
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head = head->next;
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tmp->next = new_head;
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new_head = tmp;
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}
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return new_head;
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}
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EXPORT_SYMBOL_GPL(llist_reverse_order);
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