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beaec533fc
Currently llist_for_each_entry() and llist_for_each_entry_safe() iterate until &pos->member != NULL. But when building the kernel with Clang, the compiler assumes &pos->member cannot be NULL if the member's offset is greater than 0 (which would be equivalent to the object being non-contiguous in memory). Therefore the loop condition is always true, and the loops become infinite. To work around this, introduce the member_address_is_nonnull() macro, which casts object pointer to uintptr_t, thus letting the member pointer to be NULL. Signed-off-by: Alexander Potapenko <glider@google.com> Tested-by: Sodagudi Prasad <psodagud@codeaurora.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
242 lines
9.2 KiB
C
242 lines
9.2 KiB
C
#ifndef LLIST_H
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#define LLIST_H
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/*
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* Lock-less NULL terminated single linked list
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*
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* Cases where locking is not needed:
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* If there are multiple producers and multiple consumers, llist_add can be
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* used in producers and llist_del_all can be used in consumers simultaneously
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* without locking. Also a single consumer can use llist_del_first while
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* multiple producers simultaneously use llist_add, without any locking.
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*
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* Cases where locking is needed:
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* If we have multiple consumers with llist_del_first used in one consumer, and
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* llist_del_first or llist_del_all used in other consumers, then a lock is
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* needed. This is because llist_del_first depends on list->first->next not
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* changing, but without lock protection, there's no way to be sure about that
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* if a preemption happens in the middle of the delete operation and on being
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* preempted back, the list->first is the same as before causing the cmpxchg in
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* llist_del_first to succeed. For example, while a llist_del_first operation
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* is in progress in one consumer, then a llist_del_first, llist_add,
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* llist_add (or llist_del_all, llist_add, llist_add) sequence in another
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* consumer may cause violations.
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*
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* This can be summarized as follows:
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*
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* | add | del_first | del_all
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* add | - | - | -
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* del_first | | L | L
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* del_all | | | -
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*
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* Where, a particular row's operation can happen concurrently with a column's
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* operation, with "-" being no lock needed, while "L" being lock is needed.
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*
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* The list entries deleted via llist_del_all can be traversed with
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* traversing function such as llist_for_each etc. But the list
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* entries can not be traversed safely before deleted from the list.
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* The order of deleted entries is from the newest to the oldest added
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* one. If you want to traverse from the oldest to the newest, you
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* must reverse the order by yourself before traversing.
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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/atomic.h>
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#include <linux/kernel.h>
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struct llist_head {
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struct llist_node *first;
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};
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struct llist_node {
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struct llist_node *next;
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};
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#define LLIST_HEAD_INIT(name) { NULL }
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#define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name)
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/**
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* init_llist_head - initialize lock-less list head
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* @head: the head for your lock-less list
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*/
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static inline void init_llist_head(struct llist_head *list)
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{
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list->first = NULL;
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}
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/**
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* llist_entry - get the struct of this entry
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* @ptr: the &struct llist_node pointer.
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* @type: the type of the struct this is embedded in.
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* @member: the name of the llist_node within the struct.
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*/
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#define llist_entry(ptr, type, member) \
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container_of(ptr, type, member)
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/**
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* member_address_is_nonnull - check whether the member address is not NULL
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* @ptr: the object pointer (struct type * that contains the llist_node)
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* @member: the name of the llist_node within the struct.
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*
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* This macro is conceptually the same as
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* &ptr->member != NULL
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* but it works around the fact that compilers can decide that taking a member
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* address is never a NULL pointer.
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*
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* Real objects that start at a high address and have a member at NULL are
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* unlikely to exist, but such pointers may be returned e.g. by the
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* container_of() macro.
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*/
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#define member_address_is_nonnull(ptr, member) \
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((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)
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/**
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* llist_for_each - iterate over some deleted entries of a lock-less list
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* @pos: the &struct llist_node to use as a loop cursor
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* @node: the first entry of deleted list entries
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*
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* In general, some entries of the lock-less list can be traversed
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* safely only after being deleted from list, so start with an entry
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* instead of list head.
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*
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* If being used on entries deleted from lock-less list directly, the
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* traverse order is from the newest to the oldest added entry. If
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* you want to traverse from the oldest to the newest, you must
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* reverse the order by yourself before traversing.
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*/
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#define llist_for_each(pos, node) \
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for ((pos) = (node); pos; (pos) = (pos)->next)
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/**
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* llist_for_each_safe - iterate over some deleted entries of a lock-less list
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* safe against removal of list entry
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* @pos: the &struct llist_node to use as a loop cursor
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* @n: another &struct llist_node to use as temporary storage
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* @node: the first entry of deleted list entries
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*
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* In general, some entries of the lock-less list can be traversed
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* safely only after being deleted from list, so start with an entry
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* instead of list head.
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*
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* If being used on entries deleted from lock-less list directly, the
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* traverse order is from the newest to the oldest added entry. If
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* you want to traverse from the oldest to the newest, you must
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* reverse the order by yourself before traversing.
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*/
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#define llist_for_each_safe(pos, n, node) \
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for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
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/**
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* llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
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* @pos: the type * to use as a loop cursor.
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* @node: the fist entry of deleted list entries.
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* @member: the name of the llist_node with the struct.
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*
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* In general, some entries of the lock-less list can be traversed
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* safely only after being removed from list, so start with an entry
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* instead of list head.
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*
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* If being used on entries deleted from lock-less list directly, the
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* traverse order is from the newest to the oldest added entry. If
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* you want to traverse from the oldest to the newest, you must
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* reverse the order by yourself before traversing.
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*/
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#define llist_for_each_entry(pos, node, member) \
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for ((pos) = llist_entry((node), typeof(*(pos)), member); \
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member_address_is_nonnull(pos, member); \
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(pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
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/**
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* llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
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* safe against removal of list entry
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* @pos: the type * to use as a loop cursor.
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* @n: another type * to use as temporary storage
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* @node: the first entry of deleted list entries.
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* @member: the name of the llist_node with the struct.
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*
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* In general, some entries of the lock-less list can be traversed
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* safely only after being removed from list, so start with an entry
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* instead of list head.
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*
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* If being used on entries deleted from lock-less list directly, the
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* traverse order is from the newest to the oldest added entry. If
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* you want to traverse from the oldest to the newest, you must
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* reverse the order by yourself before traversing.
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*/
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#define llist_for_each_entry_safe(pos, n, node, member) \
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for (pos = llist_entry((node), typeof(*pos), member); \
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member_address_is_nonnull(pos, member) && \
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(n = llist_entry(pos->member.next, typeof(*n), member), true); \
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pos = n)
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/**
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* llist_empty - tests whether a lock-less list is empty
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* @head: the list to test
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*
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* Not guaranteed to be accurate or up to date. Just a quick way to
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* test whether the list is empty without deleting something from the
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* list.
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*/
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static inline bool llist_empty(const struct llist_head *head)
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{
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return ACCESS_ONCE(head->first) == NULL;
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}
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static inline struct llist_node *llist_next(struct llist_node *node)
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{
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return node->next;
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}
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extern bool llist_add_batch(struct llist_node *new_first,
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struct llist_node *new_last,
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struct llist_head *head);
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/**
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* llist_add - add a new entry
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* @new: new entry to be added
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* @head: the head for your lock-less list
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*
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* Returns true if the list was empty prior to adding this entry.
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*/
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static inline bool llist_add(struct llist_node *new, struct llist_head *head)
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{
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return llist_add_batch(new, new, head);
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}
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/**
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* llist_del_all - delete all entries from lock-less list
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* @head: the head of lock-less list to delete all entries
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*
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* If list is empty, return NULL, otherwise, delete all entries and
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* return the pointer to the first entry. The order of entries
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* deleted is from the newest to the oldest added one.
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*/
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static inline struct llist_node *llist_del_all(struct llist_head *head)
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{
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return xchg(&head->first, NULL);
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}
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extern struct llist_node *llist_del_first(struct llist_head *head);
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struct llist_node *llist_reverse_order(struct llist_node *head);
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#endif /* LLIST_H */
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