I have confirmed the theory using a sample code like :
spin_lock(&a);
spin_lock(&b);
cond_resched_lock(&b);
spin_unlock(&b);
spin_unlock(&a);
Also, the following patch solves the problem for me.
----8>-----
sched: Fix ___might_sleep preempt count checks
___might_sleep checks if the preempt_count equals the passed in
preempt_offset to issue a warning. This could cause false warnings,
when preempt_count is greater than the requested offset. Fix the
check to make sure we handle this case.
e.g, following code sequence could cause false warning:
foo:
spin_lock(&a);
...
bar() ---------> bar:
spin_lock(&b);
cond_resched_lock(&b);
do_something();
spin_unlock(&b);
<-----------
...
spin_unlock(&a)
where locks a and b need not necessarily be related.
Cc: Marc Zyngier <marc.zyng...@arm.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Arnd Bergmann <a...@arndb.de>
Reported-by: Mark Rutland <mark.rutl...@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com>
---
kernel/sched/core.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3b31fc0..28842dc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6144,11 +6144,11 @@ void __init sched_init(void)
}
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
-static inline int preempt_count_equals(int preempt_offset)
+static inline int preempt_count_safe(int preempt_offset)
{
int nested = preempt_count() + rcu_preempt_depth();
- return (nested == preempt_offset);
+ return (nested >= preempt_offset);
}
void __might_sleep(const char *file, int line, int preempt_offset)
@@ -6179,7 +6179,7 @@ void ___might_sleep(const char *file, int line, int
preempt_offset)
/* WARN_ON_ONCE() by default, no rate limit required: */
rcu_sleep_check();
- if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
+ if ((preempt_count_safe(preempt_offset) && !irqs_disabled() &&
!is_idle_task(current)) ||
system_state != SYSTEM_RUNNING || oops_in_progress)
return;
@@ -6205,7 +6205,7 @@ void ___might_sleep(const char *file, int line, int
preempt_offset)
if (irqs_disabled())
print_irqtrace_events(current);
if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)
- && !preempt_count_equals(preempt_offset)) {
+ && !preempt_count_safe(preempt_offset)) {
pr_err("Preemption disabled at:");
print_ip_sym(preempt_disable_ip);
pr_cont("\n");
--
2.7.4
