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Subject[PATCH RT 3/9][RFC] [PATCH 3/9] lglock/rt: Use non-rt for_each_cpu() in -rt code
Currently the RT version of the lglocks() does a for_each_online_cpu()
in the name##_global_lock_online() functions. Non-rt uses its own
mask for this, and for good reason.

A task may grab a *_global_lock_online(), and in the mean time, one
of the CPUs goes offline. Now when that task does a *_global_unlock_online()
it releases all the locks *except* the one that went offline.

Now if that CPU were to come back on line, its lock is now owned by a
task that never released it when it should have.

This causes all sorts of fun errors. Like owners of a lock no longer
existing, or sleeping on IO, waiting to be woken up by a task that
happens to be blocked on the lock it never released.

Convert the RT versions to use the lglock specific cpumasks. As once
a CPU comes on line, the mask is set, and never cleared even when the
CPU goes offline. The locks for that CPU will still be taken and released.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
include/linux/lglock.h | 35 ++++++++++++++++++++++++++++++++---
1 files changed, 32 insertions(+), 3 deletions(-)
diff --git a/include/linux/lglock.h b/include/linux/lglock.h
index 52b289f..cdfcef3 100644
--- a/include/linux/lglock.h
+++ b/include/linux/lglock.h
@@ -203,9 +203,31 @@
#else /* !PREEMPT_RT_FULL */
#define DEFINE_LGLOCK(name) \
\
- DEFINE_PER_CPU(struct rt_mutex, name##_lock); \
+ DEFINE_PER_CPU(struct rt_mutex, name##_lock); \
+ DEFINE_SPINLOCK(name##_cpu_lock); \
+ cpumask_t name##_cpus __read_mostly; \
DEFINE_LGLOCK_LOCKDEP(name); \
\
+ static int \
+ name##_lg_cpu_callback(struct notifier_block *nb, \
+ unsigned long action, void *hcpu) \
+ { \
+ switch (action & ~CPU_TASKS_FROZEN) { \
+ case CPU_UP_PREPARE: \
+ spin_lock(&name##_cpu_lock); \
+ cpu_set((unsigned long)hcpu, name##_cpus); \
+ spin_unlock(&name##_cpu_lock); \
+ break; \
+ case CPU_UP_CANCELED: case CPU_DEAD: \
+ spin_lock(&name##_cpu_lock); \
+ cpu_clear((unsigned long)hcpu, name##_cpus); \
+ spin_unlock(&name##_cpu_lock); \
+ } \
+ return NOTIFY_OK; \
+ } \
+ static struct notifier_block name##_lg_cpu_notifier = { \
+ .notifier_call = name##_lg_cpu_callback, \
+ }; \
void name##_lock_init(void) { \
int i; \
LOCKDEP_INIT_MAP(&name##_lock_dep_map, #name, &name##_lock_key, 0); \
@@ -214,6 +236,11 @@
lock = &per_cpu(name##_lock, i); \
rt_mutex_init(lock); \
} \
+ register_hotcpu_notifier(&name##_lg_cpu_notifier); \
+ get_online_cpus(); \
+ for_each_online_cpu(i) \
+ cpu_set(i, name##_cpus); \
+ put_online_cpus(); \
} \
EXPORT_SYMBOL(name##_lock_init); \
\
@@ -254,7 +281,8 @@
void name##_global_lock_online(void) { \
int i; \
rwlock_acquire(&name##_lock_dep_map, 0, 0, _RET_IP_); \
- for_each_online_cpu(i) { \
+ spin_lock(&name##_cpu_lock); \
+ for_each_cpu(i, &name##_cpus) { \
struct rt_mutex *lock; \
lock = &per_cpu(name##_lock, i); \
__rt_spin_lock(lock); \
@@ -265,11 +293,12 @@
void name##_global_unlock_online(void) { \
int i; \
rwlock_release(&name##_lock_dep_map, 1, _RET_IP_); \
- for_each_online_cpu(i) { \
+ for_each_cpu(i, &name##_cpus) { \
struct rt_mutex *lock; \
lock = &per_cpu(name##_lock, i); \
__rt_spin_unlock(lock); \
} \
+ spin_unlock(&name##_cpu_lock); \
} \
EXPORT_SYMBOL(name##_global_unlock_online); \
\
--
1.7.3.4



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