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Update llist code

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This fixes a bug where the compiler was dropping a null ptr check
This commit is contained in:
Kent Overstreet 2019-08-28 11:35:00 -04:00
parent e6e7d374e7
commit 8192cc8ed8
2 changed files with 64 additions and 48 deletions
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96
include/linux/llist.h
View File

@ -1,31 +1,36 @@
#ifndef __TOOLS_LINUX_LLIST_H
#define __TOOLS_LINUX_LLIST_H
/* SPDX-License-Identifier: GPL-2.0-only */
#ifndef LLIST_H
#define LLIST_H
/*
* Lock-less NULL terminated single linked list
*
* If there are multiple producers and multiple consumers, llist_add
* can be used in producers and llist_del_all can be used in
* consumers. They can work simultaneously without lock. But
* llist_del_first can not be used here. Because llist_del_first
* depends on list->first->next does not changed if list->first is not
* changed during its operation, but llist_del_first, llist_add,
* llist_add (or llist_del_all, llist_add, llist_add) sequence in
* another consumer may violate that.
* Cases where locking is not needed:
* If there are multiple producers and multiple consumers, llist_add can be
* used in producers and llist_del_all can be used in consumers simultaneously
* without locking. Also a single consumer can use llist_del_first while
* multiple producers simultaneously use llist_add, without any locking.
*
* If there are multiple producers and one consumer, llist_add can be
* used in producers and llist_del_all or llist_del_first can be used
* in the consumer.
* Cases where locking is needed:
* If we have multiple consumers with llist_del_first used in one consumer, and
* llist_del_first or llist_del_all used in other consumers, then a lock is
* needed. This is because llist_del_first depends on list->first->next not
* changing, but without lock protection, there's no way to be sure about that
* if a preemption happens in the middle of the delete operation and on being
* preempted back, the list->first is the same as before causing the cmpxchg in
* llist_del_first to succeed. For example, while a llist_del_first operation
* is in progress in one consumer, then a llist_del_first, llist_add,
* llist_add (or llist_del_all, llist_add, llist_add) sequence in another
* consumer may cause violations.
*
* This can be summarized as follow:
* This can be summarized as follows:
*
* | add | del_first | del_all
* add | - | - | -
* del_first | | L | L
* del_all | | | -
*
* Where "-" stands for no lock is needed, while "L" stands for lock
* is needed.
* Where, a particular row's operation can happen concurrently with a column's
* operation, with "-" being no lock needed, while "L" being lock is needed.
*
* The list entries deleted via llist_del_all can be traversed with
* traversing function such as llist_for_each etc. But the list
@ -41,19 +46,6 @@
*
* Copyright 2010,2011 Intel Corp.
* Author: Huang Ying <ying.huang@intel.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version
* 2 as published by the Free Software Foundation;
*
* 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
*/
#include <linux/atomic.h>
@ -88,6 +80,23 @@ static inline void init_llist_head(struct llist_head *list)
#define llist_entry(ptr, type, member) \
container_of(ptr, type, member)
/**
* member_address_is_nonnull - check whether the member address is not NULL
* @ptr: the object pointer (struct type * that contains the llist_node)
* @member: the name of the llist_node within the struct.
*
* This macro is conceptually the same as
* &ptr->member != NULL
* but it works around the fact that compilers can decide that taking a member
* address is never a NULL pointer.
*
* Real objects that start at a high address and have a member at NULL are
* unlikely to exist, but such pointers may be returned e.g. by the
* container_of() macro.
*/
#define member_address_is_nonnull(ptr, member) \
((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)
/**
* llist_for_each - iterate over some deleted entries of a lock-less list
* @pos: the &struct llist_node to use as a loop cursor
@ -105,6 +114,25 @@ static inline void init_llist_head(struct llist_head *list)
#define llist_for_each(pos, node) \
for ((pos) = (node); pos; (pos) = (pos)->next)
/**
* llist_for_each_safe - iterate over some deleted entries of a lock-less list
* safe against removal of list entry
* @pos: the &struct llist_node to use as a loop cursor
* @n: another &struct llist_node to use as temporary storage
* @node: the first entry of deleted list entries
*
* In general, some entries of the lock-less list can be traversed
* safely only after being deleted from list, so start with an entry
* instead of list head.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
* you want to traverse from the oldest to the newest, you must
* reverse the order by yourself before traversing.
*/
#define llist_for_each_safe(pos, n, node) \
for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
/**
* llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
* @pos: the type * to use as a loop cursor.
@ -122,7 +150,7 @@ static inline void init_llist_head(struct llist_head *list)
*/
#define llist_for_each_entry(pos, node, member) \
for ((pos) = llist_entry((node), typeof(*(pos)), member); \
&(pos)->member != NULL; \
member_address_is_nonnull(pos, member); \
(pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
/**
@ -144,7 +172,7 @@ static inline void init_llist_head(struct llist_head *list)
*/
#define llist_for_each_entry_safe(pos, n, node, member) \
for (pos = llist_entry((node), typeof(*pos), member); \
&pos->member != NULL && \
member_address_is_nonnull(pos, member) && \
(n = llist_entry(pos->member.next, typeof(*n), member), true); \
pos = n)
@ -158,7 +186,7 @@ static inline void init_llist_head(struct llist_head *list)
*/
static inline bool llist_empty(const struct llist_head *head)
{
return ACCESS_ONCE(head->first) == NULL;
return READ_ONCE(head->first) == NULL;
}
static inline struct llist_node *llist_next(struct llist_node *node)
@ -198,4 +226,4 @@ extern struct llist_node *llist_del_first(struct llist_head *head);
struct llist_node *llist_reverse_order(struct llist_node *head);
#endif /* __TOOLS_LINUX_LLIST_H */
#endif /* LLIST_H */

16
linux/llist.c
View File

@ -1,3 +1,4 @@
// SPDX-License-Identifier: GPL-2.0-only
/*
* Lock-less NULL terminated single linked list
*
@ -8,19 +9,6 @@
*
* Copyright 2010,2011 Intel Corp.
* Author: Huang Ying <ying.huang@intel.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version
* 2 as published by the Free Software Foundation;
*
* 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
*/
#include <linux/kernel.h>
#include <linux/export.h>
@ -41,7 +29,7 @@ bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
struct llist_node *first;
do {
new_last->next = first = ACCESS_ONCE(head->first);
new_last->next = first = READ_ONCE(head->first);
} while (cmpxchg(&head->first, first, new_first) != first);
return !first;