From 82524746c27fa418c250a56dd7606b9d3fc79826 Mon Sep 17 00:00:00 2001 From: Franck Bui-Huu Date: Mon, 12 May 2008 21:21:05 +0200 Subject: rcu: split list.h and move rcu-protected lists into rculist.h Move rcu-protected lists from list.h into a new header file rculist.h. This is done because list are a very used primitive structure all over the kernel and it's currently impossible to include other header files in this list.h without creating some circular dependencies. For example, list.h implements rcu-protected list and uses rcu_dereference() without including rcupdate.h. It actually compiles because users of rcu_dereference() are macros. Others RCU functions could be used too but aren't probably because of this. Therefore this patch creates rculist.h which includes rcupdates without to many changes/troubles. Signed-off-by: Franck Bui-Huu Acked-by: Paul E. McKenney Acked-by: Josh Triplett Signed-off-by: Andrew Morton Signed-off-by: Ingo Molnar --- include/linux/rculist.h | 396 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 396 insertions(+) create mode 100644 include/linux/rculist.h (limited to 'include/linux/rculist.h') diff --git a/include/linux/rculist.h b/include/linux/rculist.h new file mode 100644 index 000000000000..aa9b3eb15683 --- /dev/null +++ b/include/linux/rculist.h @@ -0,0 +1,396 @@ +#ifndef _LINUX_RCULIST_H +#define _LINUX_RCULIST_H + +#ifdef __KERNEL__ + +/* + * RCU-protected list version + */ +#include + +/* + * Insert a new entry between two known consecutive entries. + * + * This is only for internal list manipulation where we know + * the prev/next entries already! + */ +static inline void __list_add_rcu(struct list_head *new, + struct list_head *prev, struct list_head *next) +{ + new->next = next; + new->prev = prev; + smp_wmb(); + next->prev = new; + prev->next = new; +} + +/** + * list_add_rcu - add a new entry to rcu-protected list + * @new: new entry to be added + * @head: list head to add it after + * + * Insert a new entry after the specified head. + * This is good for implementing stacks. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as list_add_rcu() + * or list_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * list_for_each_entry_rcu(). + */ +static inline void list_add_rcu(struct list_head *new, struct list_head *head) +{ + __list_add_rcu(new, head, head->next); +} + +/** + * list_add_tail_rcu - add a new entry to rcu-protected list + * @new: new entry to be added + * @head: list head to add it before + * + * Insert a new entry before the specified head. + * This is useful for implementing queues. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as list_add_tail_rcu() + * or list_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * list_for_each_entry_rcu(). + */ +static inline void list_add_tail_rcu(struct list_head *new, + struct list_head *head) +{ + __list_add_rcu(new, head->prev, head); +} + +/** + * list_del_rcu - deletes entry from list without re-initialization + * @entry: the element to delete from the list. + * + * Note: list_empty() on entry does not return true after this, + * the entry is in an undefined state. It is useful for RCU based + * lockfree traversal. + * + * In particular, it means that we can not poison the forward + * pointers that may still be used for walking the list. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as list_del_rcu() + * or list_add_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * list_for_each_entry_rcu(). + * + * Note that the caller is not permitted to immediately free + * the newly deleted entry. Instead, either synchronize_rcu() + * or call_rcu() must be used to defer freeing until an RCU + * grace period has elapsed. + */ +static inline void list_del_rcu(struct list_head *entry) +{ + __list_del(entry->prev, entry->next); + entry->prev = LIST_POISON2; +} + +/** + * list_replace_rcu - replace old entry by new one + * @old : the element to be replaced + * @new : the new element to insert + * + * The @old entry will be replaced with the @new entry atomically. + * Note: @old should not be empty. + */ +static inline void list_replace_rcu(struct list_head *old, + struct list_head *new) +{ + new->next = old->next; + new->prev = old->prev; + smp_wmb(); + new->next->prev = new; + new->prev->next = new; + old->prev = LIST_POISON2; +} + +/** + * list_splice_init_rcu - splice an RCU-protected list into an existing list. + * @list: the RCU-protected list to splice + * @head: the place in the list to splice the first list into + * @sync: function to sync: synchronize_rcu(), synchronize_sched(), ... + * + * @head can be RCU-read traversed concurrently with this function. + * + * Note that this function blocks. + * + * Important note: the caller must take whatever action is necessary to + * prevent any other updates to @head. In principle, it is possible + * to modify the list as soon as sync() begins execution. + * If this sort of thing becomes necessary, an alternative version + * based on call_rcu() could be created. But only if -really- + * needed -- there is no shortage of RCU API members. + */ +static inline void list_splice_init_rcu(struct list_head *list, + struct list_head *head, + void (*sync)(void)) +{ + struct list_head *first = list->next; + struct list_head *last = list->prev; + struct list_head *at = head->next; + + if (list_empty(head)) + return; + + /* "first" and "last" tracking list, so initialize it. */ + + INIT_LIST_HEAD(list); + + /* + * At this point, the list body still points to the source list. + * Wait for any readers to finish using the list before splicing + * the list body into the new list. Any new readers will see + * an empty list. + */ + + sync(); + + /* + * Readers are finished with the source list, so perform splice. + * The order is important if the new list is global and accessible + * to concurrent RCU readers. Note that RCU readers are not + * permitted to traverse the prev pointers without excluding + * this function. + */ + + last->next = at; + smp_wmb(); + head->next = first; + first->prev = head; + at->prev = last; +} + +/** + * list_for_each_rcu - iterate over an rcu-protected list + * @pos: the &struct list_head to use as a loop cursor. + * @head: the head for your list. + * + * This list-traversal primitive may safely run concurrently with + * the _rcu list-mutation primitives such as list_add_rcu() + * as long as the traversal is guarded by rcu_read_lock(). + */ +#define list_for_each_rcu(pos, head) \ + for (pos = (head)->next; \ + prefetch(rcu_dereference(pos)->next), pos != (head); \ + pos = pos->next) + +#define __list_for_each_rcu(pos, head) \ + for (pos = (head)->next; \ + rcu_dereference(pos) != (head); \ + pos = pos->next) + +/** + * list_for_each_safe_rcu + * @pos: the &struct list_head to use as a loop cursor. + * @n: another &struct list_head to use as temporary storage + * @head: the head for your list. + * + * Iterate over an rcu-protected list, safe against removal of list entry. + * + * This list-traversal primitive may safely run concurrently with + * the _rcu list-mutation primitives such as list_add_rcu() + * as long as the traversal is guarded by rcu_read_lock(). + */ +#define list_for_each_safe_rcu(pos, n, head) \ + for (pos = (head)->next; \ + n = rcu_dereference(pos)->next, pos != (head); \ + pos = n) + +/** + * list_for_each_entry_rcu - iterate over rcu list of given type + * @pos: the type * to use as a loop cursor. + * @head: the head for your list. + * @member: the name of the list_struct within the struct. + * + * This list-traversal primitive may safely run concurrently with + * the _rcu list-mutation primitives such as list_add_rcu() + * as long as the traversal is guarded by rcu_read_lock(). + */ +#define list_for_each_entry_rcu(pos, head, member) \ + for (pos = list_entry((head)->next, typeof(*pos), member); \ + prefetch(rcu_dereference(pos)->member.next), \ + &pos->member != (head); \ + pos = list_entry(pos->member.next, typeof(*pos), member)) + + +/** + * list_for_each_continue_rcu + * @pos: the &struct list_head to use as a loop cursor. + * @head: the head for your list. + * + * Iterate over an rcu-protected list, continuing after current point. + * + * This list-traversal primitive may safely run concurrently with + * the _rcu list-mutation primitives such as list_add_rcu() + * as long as the traversal is guarded by rcu_read_lock(). + */ +#define list_for_each_continue_rcu(pos, head) \ + for ((pos) = (pos)->next; \ + prefetch(rcu_dereference((pos))->next), (pos) != (head); \ + (pos) = (pos)->next) + +/** + * hlist_del_rcu - deletes entry from hash list without re-initialization + * @n: the element to delete from the hash list. + * + * Note: list_unhashed() on entry does not return true after this, + * the entry is in an undefined state. It is useful for RCU based + * lockfree traversal. + * + * In particular, it means that we can not poison the forward + * pointers that may still be used for walking the hash list. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as hlist_add_head_rcu() + * or hlist_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * hlist_for_each_entry(). + */ +static inline void hlist_del_rcu(struct hlist_node *n) +{ + __hlist_del(n); + n->pprev = LIST_POISON2; +} + +/** + * hlist_replace_rcu - replace old entry by new one + * @old : the element to be replaced + * @new : the new element to insert + * + * The @old entry will be replaced with the @new entry atomically. + */ +static inline void hlist_replace_rcu(struct hlist_node *old, + struct hlist_node *new) +{ + struct hlist_node *next = old->next; + + new->next = next; + new->pprev = old->pprev; + smp_wmb(); + if (next) + new->next->pprev = &new->next; + *new->pprev = new; + old->pprev = LIST_POISON2; +} + +/** + * hlist_add_head_rcu + * @n: the element to add to the hash list. + * @h: the list to add to. + * + * Description: + * Adds the specified element to the specified hlist, + * while permitting racing traversals. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as hlist_add_head_rcu() + * or hlist_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * hlist_for_each_entry_rcu(), used to prevent memory-consistency + * problems on Alpha CPUs. Regardless of the type of CPU, the + * list-traversal primitive must be guarded by rcu_read_lock(). + */ +static inline void hlist_add_head_rcu(struct hlist_node *n, + struct hlist_head *h) +{ + struct hlist_node *first = h->first; + n->next = first; + n->pprev = &h->first; + smp_wmb(); + if (first) + first->pprev = &n->next; + h->first = n; +} + +/** + * hlist_add_before_rcu + * @n: the new element to add to the hash list. + * @next: the existing element to add the new element before. + * + * Description: + * Adds the specified element to the specified hlist + * before the specified node while permitting racing traversals. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as hlist_add_head_rcu() + * or hlist_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * hlist_for_each_entry_rcu(), used to prevent memory-consistency + * problems on Alpha CPUs. + */ +static inline void hlist_add_before_rcu(struct hlist_node *n, + struct hlist_node *next) +{ + n->pprev = next->pprev; + n->next = next; + smp_wmb(); + next->pprev = &n->next; + *(n->pprev) = n; +} + +/** + * hlist_add_after_rcu + * @prev: the existing element to add the new element after. + * @n: the new element to add to the hash list. + * + * Description: + * Adds the specified element to the specified hlist + * after the specified node while permitting racing traversals. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as hlist_add_head_rcu() + * or hlist_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * hlist_for_each_entry_rcu(), used to prevent memory-consistency + * problems on Alpha CPUs. + */ +static inline void hlist_add_after_rcu(struct hlist_node *prev, + struct hlist_node *n) +{ + n->next = prev->next; + n->pprev = &prev->next; + smp_wmb(); + prev->next = n; + if (n->next) + n->next->pprev = &n->next; +} + +/** + * hlist_for_each_entry_rcu - iterate over rcu list of given type + * @tpos: the type * to use as a loop cursor. + * @pos: the &struct hlist_node to use as a loop cursor. + * @head: the head for your list. + * @member: the name of the hlist_node within the struct. + * + * This list-traversal primitive may safely run concurrently with + * the _rcu list-mutation primitives such as hlist_add_head_rcu() + * as long as the traversal is guarded by rcu_read_lock(). + */ +#define hlist_for_each_entry_rcu(tpos, pos, head, member) \ + for (pos = (head)->first; \ + rcu_dereference(pos) && ({ prefetch(pos->next); 1; }) && \ + ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \ + pos = pos->next) + +#endif /* __KERNEL__ */ +#endif -- cgit v1.2.3 From 10aa9d2cf9878757b003023d33ff90a37aa3044b Mon Sep 17 00:00:00 2001 From: Franck Bui-Huu Date: Mon, 12 May 2008 21:21:06 +0200 Subject: rculist.h: use the rcu API Make almost all list mutation primitives use rcu_assign_pointer(). The main point of this being readability improvement. Signed-off-by: Franck Bui-Huu Cc: "Paul E. McKenney" Cc: Josh Triplett Signed-off-by: Andrew Morton Signed-off-by: Ingo Molnar --- include/linux/rculist.h | 23 +++++++++-------------- 1 file changed, 9 insertions(+), 14 deletions(-) (limited to 'include/linux/rculist.h') diff --git a/include/linux/rculist.h b/include/linux/rculist.h index aa9b3eb15683..8d2c81fccfe5 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -7,6 +7,7 @@ * RCU-protected list version */ #include +#include /* * Insert a new entry between two known consecutive entries. @@ -19,9 +20,8 @@ static inline void __list_add_rcu(struct list_head *new, { new->next = next; new->prev = prev; - smp_wmb(); + rcu_assign_pointer(prev->next, new); next->prev = new; - prev->next = new; } /** @@ -110,9 +110,8 @@ static inline void list_replace_rcu(struct list_head *old, { new->next = old->next; new->prev = old->prev; - smp_wmb(); + rcu_assign_pointer(new->prev->next, new); new->next->prev = new; - new->prev->next = new; old->prev = LIST_POISON2; } @@ -166,8 +165,7 @@ static inline void list_splice_init_rcu(struct list_head *list, */ last->next = at; - smp_wmb(); - head->next = first; + rcu_assign_pointer(head->next, first); first->prev = head; at->prev = last; } @@ -280,10 +278,9 @@ static inline void hlist_replace_rcu(struct hlist_node *old, new->next = next; new->pprev = old->pprev; - smp_wmb(); + rcu_assign_pointer(*new->pprev, new); if (next) new->next->pprev = &new->next; - *new->pprev = new; old->pprev = LIST_POISON2; } @@ -310,12 +307,12 @@ static inline void hlist_add_head_rcu(struct hlist_node *n, struct hlist_head *h) { struct hlist_node *first = h->first; + n->next = first; n->pprev = &h->first; - smp_wmb(); + rcu_assign_pointer(h->first, n); if (first) first->pprev = &n->next; - h->first = n; } /** @@ -341,9 +338,8 @@ static inline void hlist_add_before_rcu(struct hlist_node *n, { n->pprev = next->pprev; n->next = next; - smp_wmb(); + rcu_assign_pointer(*(n->pprev), n); next->pprev = &n->next; - *(n->pprev) = n; } /** @@ -369,8 +365,7 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev, { n->next = prev->next; n->pprev = &prev->next; - smp_wmb(); - prev->next = n; + rcu_assign_pointer(prev->next, n); if (n->next) n->next->pprev = &n->next; } -- cgit v1.2.3 From 78b0e0e9b27b62c4b22f05a147f7a80fa58b1ae3 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 12 May 2008 21:21:06 +0200 Subject: RCU, rculist.h: fix list iterators RCU list iterators: should prefetch ever be optimised out with no side-effects, the current version will lose the barrier completely. Pointed-out-by: Linus Torvalds Signed-off-by: Paul E. McKenney Signed-off-by: Ingo Molnar --- include/linux/rculist.h | 48 +++++++++++++++--------------------------------- 1 file changed, 15 insertions(+), 33 deletions(-) (limited to 'include/linux/rculist.h') diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 8d2c81fccfe5..b0f39be08b6c 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -180,31 +180,14 @@ static inline void list_splice_init_rcu(struct list_head *list, * as long as the traversal is guarded by rcu_read_lock(). */ #define list_for_each_rcu(pos, head) \ - for (pos = (head)->next; \ - prefetch(rcu_dereference(pos)->next), pos != (head); \ - pos = pos->next) + for (pos = rcu_dereference((head)->next); \ + prefetch(pos->next), pos != (head); \ + pos = rcu_dereference(pos->next)) #define __list_for_each_rcu(pos, head) \ - for (pos = (head)->next; \ - rcu_dereference(pos) != (head); \ - pos = pos->next) - -/** - * list_for_each_safe_rcu - * @pos: the &struct list_head to use as a loop cursor. - * @n: another &struct list_head to use as temporary storage - * @head: the head for your list. - * - * Iterate over an rcu-protected list, safe against removal of list entry. - * - * This list-traversal primitive may safely run concurrently with - * the _rcu list-mutation primitives such as list_add_rcu() - * as long as the traversal is guarded by rcu_read_lock(). - */ -#define list_for_each_safe_rcu(pos, n, head) \ - for (pos = (head)->next; \ - n = rcu_dereference(pos)->next, pos != (head); \ - pos = n) + for (pos = rcu_dereference((head)->next); \ + pos != (head); \ + pos = rcu_dereference(pos->next)) /** * list_for_each_entry_rcu - iterate over rcu list of given type @@ -217,10 +200,9 @@ static inline void list_splice_init_rcu(struct list_head *list, * as long as the traversal is guarded by rcu_read_lock(). */ #define list_for_each_entry_rcu(pos, head, member) \ - for (pos = list_entry((head)->next, typeof(*pos), member); \ - prefetch(rcu_dereference(pos)->member.next), \ - &pos->member != (head); \ - pos = list_entry(pos->member.next, typeof(*pos), member)) + for (pos = list_entry(rcu_dereference((head)->next), typeof(*pos), member); \ + prefetch(pos->member.next), &pos->member != (head); \ + pos = list_entry(rcu_dereference(pos->member.next), typeof(*pos), member)) /** @@ -235,9 +217,9 @@ static inline void list_splice_init_rcu(struct list_head *list, * as long as the traversal is guarded by rcu_read_lock(). */ #define list_for_each_continue_rcu(pos, head) \ - for ((pos) = (pos)->next; \ - prefetch(rcu_dereference((pos))->next), (pos) != (head); \ - (pos) = (pos)->next) + for ((pos) = rcu_dereference((pos)->next); \ + prefetch((pos)->next), (pos) != (head); \ + (pos) = rcu_dereference((pos)->next)) /** * hlist_del_rcu - deletes entry from hash list without re-initialization @@ -382,10 +364,10 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev, * as long as the traversal is guarded by rcu_read_lock(). */ #define hlist_for_each_entry_rcu(tpos, pos, head, member) \ - for (pos = (head)->first; \ - rcu_dereference(pos) && ({ prefetch(pos->next); 1; }) && \ + for (pos = rcu_dereference((head)->first); \ + pos && ({ prefetch(pos->next); 1; }) && \ ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \ - pos = pos->next) + pos = rcu_dereference(pos->next)) #endif /* __KERNEL__ */ #endif -- cgit v1.2.3