This adds an overhead of a function call and local_irq_save/restore
in the rcu reader path when CONFIG_DEBUG_SPINLOCK_SLEEP is set.
Hopefully that is not much of a concern. Comments are welcome.
Applies on top of my earlier patches. The full patchset is
at http://www.hill9.org/linux/kernel/patches/2.6.18-mm1/.
Add a debug check for rcu read-side critical section code calling
a function that might sleep which is illegal. The check is enabled only
if CONFIG_DEBUG_SPINLOCK_SLEEP is set.
Signed-off-by: Dipankar Sarma <[email protected]>
---
include/linux/rcupdate.h | 34 ++++++++++++++++++++++++++++++----
kernel/rcupdate.c | 33 +++++++++++++++++++++++++++++++++
kernel/sched.c | 2 +-
3 files changed, 64 insertions(+), 5 deletions(-)
diff -puN include/linux/rcupdate.h~rcu-reader-sleep-check include/linux/rcupdate.h
--- linux-2.6.18-mm1-rcu/include/linux/rcupdate.h~rcu-reader-sleep-check 2006-09-24 23:18:35.000000000 +0530
+++ linux-2.6.18-mm1-rcu-dipankar/include/linux/rcupdate.h 2006-09-24 23:18:35.000000000 +0530
@@ -64,6 +64,16 @@ struct rcu_head {
(ptr)->next = NULL; (ptr)->func = NULL; \
} while (0)
+#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
+extern int rcu_read_in_atomic(void);
+extern void rcu_add_read_count(void);
+extern void rcu_sub_read_count(void);
+#else
+static inline int rcu_read_in_atomic(void) { return 0;}
+static inline void rcu_add_read_count(void) {}
+static inline void rcu_sub_read_count(void) {}
+#endif
+
/**
* rcu_read_lock - mark the beginning of an RCU read-side critical section.
*
@@ -93,14 +103,22 @@ struct rcu_head {
*
* It is illegal to block while in an RCU read-side critical section.
*/
-#define rcu_read_lock() __rcu_read_lock()
+#define rcu_read_lock() \
+ do { \
+ rcu_add_read_count(); \
+ __rcu_read_lock(); \
+ } while (0)
/**
* rcu_read_unlock - marks the end of an RCU read-side critical section.
*
* See rcu_read_lock() for more information.
*/
-#define rcu_read_unlock() __rcu_read_unlock()
+#define rcu_read_unlock() \
+ do { \
+ __rcu_read_unlock(); \
+ rcu_sub_read_count(); \
+ } while (0)
/*
* So where is rcu_write_lock()? It does not exist, as there is no
@@ -123,14 +141,22 @@ struct rcu_head {
* can use just rcu_read_lock().
*
*/
-#define rcu_read_lock_bh() __rcu_read_lock_bh()
+#define rcu_read_lock_bh() \
+ do { \
+ rcu_add_read_count(); \
+ __rcu_read_lock_bh(); \
+ } while (0)
/**
* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
*
* See rcu_read_lock_bh() for more information.
*/
-#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
+#define rcu_read_unlock_bh() \
+ do { \
+ __rcu_read_unlock_bh(); \
+ rcu_sub_read_count(); \
+ } while (0)
/**
* rcu_dereference - fetch an RCU-protected pointer in an
diff -puN kernel/rcupdate.c~rcu-reader-sleep-check kernel/rcupdate.c
--- linux-2.6.18-mm1-rcu/kernel/rcupdate.c~rcu-reader-sleep-check 2006-09-24 23:18:35.000000000 +0530
+++ linux-2.6.18-mm1-rcu-dipankar/kernel/rcupdate.c 2006-09-24 23:18:35.000000000 +0530
@@ -127,5 +127,38 @@ void __init rcu_init(void)
__rcu_init();
}
+#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
+DEFINE_PER_CPU(int, rcu_read_count);
+int rcu_read_in_atomic(void)
+{
+ int val;
+ int cpu = get_cpu();
+ val = per_cpu(rcu_read_count, cpu);
+ put_cpu();
+ return val;
+}
+
+void rcu_add_read_count(void)
+{
+ int cpu, flags;
+ local_irq_save(flags);
+ cpu = smp_processor_id();
+ per_cpu(rcu_read_count, cpu)++;
+ local_irq_restore(flags);
+}
+
+void rcu_sub_read_count(void)
+{
+ int cpu, flags;
+ local_irq_save(flags);
+ cpu = smp_processor_id();
+ per_cpu(rcu_read_count, cpu)--;
+ local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(rcu_read_in_atomic);
+EXPORT_SYMBOL_GPL(rcu_add_read_count);
+EXPORT_SYMBOL_GPL(rcu_sub_read_count);
+#endif
+
EXPORT_SYMBOL_GPL(rcu_barrier);
EXPORT_SYMBOL_GPL(synchronize_rcu);
diff -puN kernel/sched.c~rcu-reader-sleep-check kernel/sched.c
--- linux-2.6.18-mm1-rcu/kernel/sched.c~rcu-reader-sleep-check 2006-09-24 23:18:35.000000000 +0530
+++ linux-2.6.18-mm1-rcu-dipankar/kernel/sched.c 2006-09-24 23:18:35.000000000 +0530
@@ -6974,7 +6974,7 @@ void __might_sleep(char *file, int line)
#ifdef in_atomic
static unsigned long prev_jiffy; /* ratelimiting */
- if ((in_atomic() || irqs_disabled()) &&
+ if ((in_atomic() || irqs_disabled() || rcu_read_in_atomic()) &&
system_state == SYSTEM_RUNNING && !oops_in_progress) {
if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
return;
_
-
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