Prototypes for the proposed rcu_get_gp_cookie() / rcu_gp_cookie_elapsed() functionality as discussed in http://marc.info/?l=linux-mm&m=131316547914194 (This is not a correct implementation of the proposed API; Paul McKenney is to provide that as a follow-up to this RFC) Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx> --- include/linux/rcupdate.h | 35 +++++++++++++++++++++++++++++++++++ 1 files changed, 35 insertions(+), 0 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 99f9aa7..315a0f1 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -865,4 +865,39 @@ static inline void __rcu_reclaim(struct rcu_head *head) #define kfree_rcu(ptr, rcu_head) \ __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) +struct rcu_cookie {long x; }; + +/* + * rcu_get_gp_cookie() / rcu_gp_cookie_elapsed() + * + * rcu_get_gp_cookie() stores an opaque cookie to the provided location. + * + * rcu_gp_cookie_elapsed() returns true if it can guarantee that + * an rcu grace period has elapsed since the provided cookie was + * created by rcu_get_gp_cookie(). A return value of false indicates + * that rcu_gp_cookie_elapsed() does not know if an rcu grace period has + * elapsed or not - the call site is then expected to drop locks as desired, + * call rcu_synchronize(), and retry. + * + * Note that call sites are allowed to assume that rcu_gp_cookie_elapsed() + * will return true if they try enough times. An implementation that always + * returns false would be incorrect. + * + * The implementation below is also incorrect (may return false positives), + * however it does test that one always calls rcu_get_gp_cookie() before + * rcu_gp_cookie_elapsed() and that rcu_gp_cookie_elapsed() call sites + * are ready to handle both possible cases. + */ +static inline void rcu_get_gp_cookie(struct rcu_cookie *rcp) +{ + rcp->x = 12345678; +} + +static inline bool rcu_gp_cookie_elapsed(struct rcu_cookie *rcp) +{ + static int count = 0; + BUG_ON(rcp->x != 12345678); + return (count++ % 16) != 0; +} + #endif /* __LINUX_RCUPDATE_H */ -- 1.7.3.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>