diff options
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/rculist.h | 35 | ||||
| -rw-r--r-- | include/linux/rcupdate.h | 4 | ||||
| -rw-r--r-- | include/linux/rcutiny.h | 3 | ||||
| -rw-r--r-- | include/linux/srcutiny.h | 8 |
4 files changed, 23 insertions, 27 deletions
diff --git a/include/linux/rculist.h b/include/linux/rculist.h index f8633d37e358..d29740be4833 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -11,15 +11,6 @@ #include <linux/rcupdate.h> /* - * Why is there no list_empty_rcu()? Because list_empty() serves this - * purpose. The list_empty() function fetches the RCU-protected pointer - * and compares it to the address of the list head, but neither dereferences - * this pointer itself nor provides this pointer to the caller. Therefore, - * it is not necessary to use rcu_dereference(), so that list_empty() can - * be used anywhere you would want to use a list_empty_rcu(). - */ - -/* * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers * @list: list to be initialized * @@ -318,21 +309,29 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, /* * Where are list_empty_rcu() and list_first_entry_rcu()? * - * Implementing those functions following their counterparts list_empty() and - * list_first_entry() is not advisable because they lead to subtle race - * conditions as the following snippet shows: + * They do not exist because they would lead to subtle race conditions: * * if (!list_empty_rcu(mylist)) { * struct foo *bar = list_first_entry_rcu(mylist, struct foo, list_member); * do_something(bar); * } * - * The list may not be empty when list_empty_rcu checks it, but it may be when - * list_first_entry_rcu rereads the ->next pointer. - * - * Rereading the ->next pointer is not a problem for list_empty() and - * list_first_entry() because they would be protected by a lock that blocks - * writers. + * The list might be non-empty when list_empty_rcu() checks it, but it + * might have become empty by the time that list_first_entry_rcu() rereads + * the ->next pointer, which would result in a SEGV. + * + * When not using RCU, it is OK for list_first_entry() to re-read that + * pointer because both functions should be protected by some lock that + * blocks writers. + * + * When using RCU, list_empty() uses READ_ONCE() to fetch the + * RCU-protected ->next pointer and then compares it to the address of the + * list head. However, it neither dereferences this pointer nor provides + * this pointer to its caller. Thus, READ_ONCE() suffices (that is, + * rcu_dereference() is not needed), which means that list_empty() can be + * used anywhere you would want to use list_empty_rcu(). Just don't + * expect anything useful to happen if you do a subsequent lockless + * call to list_first_entry_rcu()!!! * * See list_first_or_null_rcu for an alternative. */ diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index d9680b798b21..434d12fe2d4f 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -53,7 +53,7 @@ void __rcu_read_unlock(void); * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. */ -#define rcu_preempt_depth() (current->rcu_read_lock_nesting) +#define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting) #else /* #ifdef CONFIG_PREEMPT_RCU */ @@ -167,7 +167,7 @@ void synchronize_rcu_tasks(void); # define synchronize_rcu_tasks synchronize_rcu # endif -# ifdef CONFIG_TASKS_RCU_TRACE +# ifdef CONFIG_TASKS_TRACE_RCU # define rcu_tasks_trace_qs(t) \ do { \ if (!likely(READ_ONCE((t)->trc_reader_checked)) && \ diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 953e70fafe38..9be015305f9f 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -14,9 +14,6 @@ #include <asm/param.h> /* for HZ */ -/* Never flag non-existent other CPUs! */ -static inline bool rcu_eqs_special_set(int cpu) { return false; } - unsigned long get_state_synchronize_rcu(void); unsigned long start_poll_synchronize_rcu(void); bool poll_state_synchronize_rcu(unsigned long oldstate); diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h index 0e0cf4d6a72a..6cfaa0a9a9b9 100644 --- a/include/linux/srcutiny.h +++ b/include/linux/srcutiny.h @@ -61,7 +61,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp) int idx; idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1; - WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1); + WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1); return idx; } @@ -81,11 +81,11 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp, { int idx; - idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1; + idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1; pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n", tt, tf, idx, - READ_ONCE(ssp->srcu_lock_nesting[!idx]), - READ_ONCE(ssp->srcu_lock_nesting[idx])); + data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])), + data_race(READ_ONCE(ssp->srcu_lock_nesting[idx]))); } #endif |