From 7ec99de36f402618ae44147ac7fa9a07e4757a5f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 30 Jun 2016 13:58:26 -0700 Subject: rcu: Provide exact CPU-online tracking for RCU Up to now, RCU has assumed that the CPU-online process makes it from CPU_UP_PREPARE to set_cpu_online() within one jiffy. Given the recent rise of virtualized environments, this assumption is very clearly obsolete. Failing to meet this deadline can result in RCU paying attention to an incoming CPU for one jiffy, then ignoring it until the grace period following the one in which that CPU sets itself online. This situation might prove to be fatally disappointing to any RCU read-side critical sections that had the misfortune to execute during the time in which RCU was ignoring the slow-to-come-online CPU. This commit therefore updates RCU's internal CPU state-tracking information at notify_cpu_starting() time, thus providing RCU with an exact transition of the CPU's state from offline to online. Note that this means that incoming CPUs must not use RCU read-side critical section (other than those of SRCU) until notify_cpu_starting() time. Note also that the CPU_STARTING notifiers -are- allowed to use RCU read-side critical sections. (Of course, CPU-hotplug notifiers are rapidly becoming obsolete, so you need to act fast!) If a given architecture or CPU family needs to use RCU read-side critical sections earlier, the call to rcu_cpu_starting() from notify_cpu_starting() will need to be architecture-specific, with architectures that need early use being required to hand-place the call to rcu_cpu_starting() at some point preceding the call to notify_cpu_starting(). Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 1aa62e1a761b..321f9ed552a9 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -334,6 +334,7 @@ void rcu_sched_qs(void); void rcu_bh_qs(void); void rcu_check_callbacks(int user); void rcu_report_dead(unsigned int cpu); +void rcu_cpu_starting(unsigned int cpu); #ifndef CONFIG_TINY_RCU void rcu_end_inkernel_boot(void); -- cgit v1.2.3 From 489bb3d252d41392ce52590e49f0ae8782fb016e Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Sun, 21 Aug 2016 16:54:40 +0900 Subject: torture: TOROUT_STRING(): Insert a space between flag and message The TOROUT_STRING() macro does not insert a space between the flag and the message. In contrast, other similar torture-test dmesg messages consistently supply a single space character. This difference makes the output hard to read and to mechanically parse. This commit therefore adds a space character between flag and message in TOROUT_STRING() output. Signed-off-by: SeongJae Park Signed-off-by: Paul E. McKenney --- include/linux/torture.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/torture.h b/include/linux/torture.h index 6685a73736a2..a45702eb3e7b 100644 --- a/include/linux/torture.h +++ b/include/linux/torture.h @@ -43,7 +43,7 @@ #define TORTURE_FLAG "-torture:" #define TOROUT_STRING(s) \ - pr_alert("%s" TORTURE_FLAG s "\n", torture_type) + pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s) #define VERBOSE_TOROUT_STRING(s) \ do { if (verbose) pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s); } while (0) #define VERBOSE_TOROUT_ERRSTRING(s) \ -- cgit v1.2.3 From 12adfd882c5f37548acaba4f043a158b3c54468b Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Sat, 23 Jul 2016 19:27:50 +0100 Subject: list: Expand list_first_entry_or_null() Due to the use of READ_ONCE() in list_empty() the compiler cannot optimise !list_empty() ? list_first_entry() : NULL very well. By manually expanding list_first_entry_or_null() we can take advantage of the READ_ONCE() to avoid the list element changing under the test while the compiler can generate smaller code. Signed-off-by: Chris Wilson Cc: "Paul E. McKenney" Cc: Andrew Morton Cc: Dan Williams Cc: Jan Kara Cc: Josef Bacik Cc: linux-kernel@vger.kernel.org Signed-off-by: Paul E. McKenney --- include/linux/list.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/list.h b/include/linux/list.h index 5183138aa932..5809e9a2de5b 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -381,8 +381,11 @@ static inline void list_splice_tail_init(struct list_head *list, * * Note that if the list is empty, it returns NULL. */ -#define list_first_entry_or_null(ptr, type, member) \ - (!list_empty(ptr) ? list_first_entry(ptr, type, member) : NULL) +#define list_first_entry_or_null(ptr, type, member) ({ \ + struct list_head *head__ = (ptr); \ + struct list_head *pos__ = READ_ONCE(head__->next); \ + pos__ != head__ ? list_entry(pos__, type, member) : NULL; \ +}) /** * list_next_entry - get the next element in list -- cgit v1.2.3