From 8cf7d362c0dc2cfda2146d184eedc32a530c8020 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Fri, 17 Oct 2008 11:25:23 +0200 Subject: profiling: fix !procfs build fix: kernel/built-in.o: In function `profiling_store': ksysfs.c:(.text+0x1f90c): undefined reference to `create_proc_profile' Signed-off-by: Ingo Molnar --- include/linux/profile.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/include/linux/profile.h b/include/linux/profile.h index 570045053ce..e3eca8577a3 100644 --- a/include/linux/profile.h +++ b/include/linux/profile.h @@ -37,7 +37,14 @@ extern int prof_on __read_mostly; /* init basic kernel profiler */ int profile_init(void); int profile_setup(char *str); +#ifdef CONFIG_PROC_FS int create_proc_profile(void); +#else +static inline int create_proc_profile(void) +{ + return 0; +} +#endif void profile_tick(int type); /* -- cgit v1.2.3 From 5f86515158ca86182c1dbecd546f1848121ba135 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Fri, 17 Oct 2008 14:40:30 +0800 Subject: rcupdate: fix bug of rcu_barrier*() current rcu_barrier_bh() is like this: void rcu_barrier_bh(void) { BUG_ON(in_interrupt()); /* Take cpucontrol mutex to protect against CPU hotplug */ mutex_lock(&rcu_barrier_mutex); init_completion(&rcu_barrier_completion); atomic_set(&rcu_barrier_cpu_count, 0); /* * The queueing of callbacks in all CPUs must be atomic with * respect to RCU, otherwise one CPU may queue a callback, * wait for a grace period, decrement barrier count and call * complete(), while other CPUs have not yet queued anything. * So, we need to make sure that grace periods cannot complete * until all the callbacks are queued. */ rcu_read_lock(); on_each_cpu(rcu_barrier_func, (void *)RCU_BARRIER_BH, 1); rcu_read_unlock(); wait_for_completion(&rcu_barrier_completion); mutex_unlock(&rcu_barrier_mutex); } The inconsistency of the code and the comments show a bug here. rcu_read_lock() cannot make sure that "grace periods for RCU_BH cannot complete until all the callbacks are queued". it only make sure that race periods for RCU cannot complete until all the callbacks are queued. so we must use rcu_read_lock_bh() for rcu_barrier_bh(). like this: void rcu_barrier_bh(void) { ...... rcu_read_lock_bh(); on_each_cpu(rcu_barrier_func, (void *)RCU_BARRIER_BH, 1); rcu_read_unlock_bh(); ...... } and also rcu_barrier() rcu_barrier_sched() are implemented like this. it will bring a lot of duplicate code. My patch uses another way to fix this bug, please see the comment of my patch. Thank Paul E. McKenney for he rewrote the comment. Signed-off-by: Lai Jiangshan Reviewed-by: Paul E. McKenney Signed-off-by: Ingo Molnar --- kernel/rcupdate.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 467d5940f62..ad63af8b252 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -119,18 +119,19 @@ static void _rcu_barrier(enum rcu_barrier type) /* Take cpucontrol mutex to protect against CPU hotplug */ mutex_lock(&rcu_barrier_mutex); init_completion(&rcu_barrier_completion); - atomic_set(&rcu_barrier_cpu_count, 0); /* - * The queueing of callbacks in all CPUs must be atomic with - * respect to RCU, otherwise one CPU may queue a callback, - * wait for a grace period, decrement barrier count and call - * complete(), while other CPUs have not yet queued anything. - * So, we need to make sure that grace periods cannot complete - * until all the callbacks are queued. + * Initialize rcu_barrier_cpu_count to 1, then invoke + * rcu_barrier_func() on each CPU, so that each CPU also has + * incremented rcu_barrier_cpu_count. Only then is it safe to + * decrement rcu_barrier_cpu_count -- otherwise the first CPU + * might complete its grace period before all of the other CPUs + * did their increment, causing this function to return too + * early. */ - rcu_read_lock(); + atomic_set(&rcu_barrier_cpu_count, 1); on_each_cpu(rcu_barrier_func, (void *)type, 1); - rcu_read_unlock(); + if (atomic_dec_and_test(&rcu_barrier_cpu_count)) + complete(&rcu_barrier_completion); wait_for_completion(&rcu_barrier_completion); mutex_unlock(&rcu_barrier_mutex); } -- cgit v1.2.3