linux-kernel - Re: [RFC][PATCH 0/7] nested sleeps, fixes and debug infra

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Date:	Tue, 5 Aug 2014 15:06:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ilya Dryomov <ilya.dryomov@...tank.com>
Cc:	Ingo Molnar <mingo@...nel.org>, oleg@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	tglx@...utronix.de, Mike Galbraith <umgwanakikbuti@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH 0/7] nested sleeps, fixes and debug infra

On Tue, Aug 05, 2014 at 12:33:16PM +0400, Ilya Dryomov wrote:
> On Mon, Aug 4, 2014 at 2:30 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > Hi,
> >
> > Ilya recently tripped over a nested sleep which made Ingo suggest we should
> > have debug checks for that. So I did some, see patch 7. Of course that
> > triggered a whole bunch of fail the instant I tried to boot my machine.
> >
> > With this series I can boot my test box and build a kernel on it, I'm fairly
> > sure that's far too limited a test to have found all, but its a start.
> 
> FWIW, I'm getting a lot of these during light rbd testing.  CC'ed
> netdev and linux-mm.

Both are cond_resched() calls, and that's not blocking as such, just a
preemption point, so lets exclude those.

From the school of '_' are free:

---
 include/linux/kernel.h |    3 +++
 include/linux/sched.h  |    6 +++---
 kernel/sched/core.c    |   12 +++++++++---
 3 files changed, 15 insertions(+), 6 deletions(-)

--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -162,6 +162,7 @@ extern int _cond_resched(void);
 #endif
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
+  void ___might_sleep(const char *file, int line, int preempt_offset);
   void __might_sleep(const char *file, int line, int preempt_offset);
 /**
  * might_sleep - annotation for functions that can sleep
@@ -176,6 +177,8 @@ extern int _cond_resched(void);
 # define might_sleep() \
 	do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
 #else
+  static inline void ___might_sleep(const char *file, int line,
+				   int preempt_offset) { }
   static inline void __might_sleep(const char *file, int line,
 				   int preempt_offset) { }
 # define might_sleep() do { might_resched(); } while (0)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2754,7 +2754,7 @@ static inline int signal_pending_state(l
 extern int _cond_resched(void);
 
 #define cond_resched() ({			\
-	__might_sleep(__FILE__, __LINE__, 0);	\
+	___might_sleep(__FILE__, __LINE__, 0);	\
 	_cond_resched();			\
 })
 
@@ -2767,14 +2767,14 @@ extern int __cond_resched_lock(spinlock_
 #endif
 
 #define cond_resched_lock(lock) ({				\
-	__might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);	\
+	___might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);\
 	__cond_resched_lock(lock);				\
 })
 
 extern int __cond_resched_softirq(void);
 
 #define cond_resched_softirq() ({					\
-	__might_sleep(__FILE__, __LINE__, SOFTIRQ_DISABLE_OFFSET);	\
+	___might_sleep(__FILE__, __LINE__, SOFTIRQ_DISABLE_OFFSET);	\
 	__cond_resched_softirq();					\
 })
 
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7078,8 +7078,6 @@ static inline int preempt_count_equals(i
 
 void __might_sleep(const char *file, int line, int preempt_offset)
 {
-	static unsigned long prev_jiffy;	/* ratelimiting */
-
 	/*
 	 * Blocking primitives will set (and therefore destroy) current->state,
 	 * since we will exit with TASK_RUNNING make sure we enter with it,
@@ -7093,6 +7091,14 @@ void __might_sleep(const char *file, int
 			(void *)current->task_state_change))
 		__set_current_state(TASK_RUNNING);
 
+	___might_sleep(file, line, preempt_offset);
+}
+EXPORT_SYMBOL(__might_sleep);
+
+void ___might_sleep(const char *file, int line, int preempt_offset)
+{
+	static unsigned long prev_jiffy;	/* ratelimiting */
+
 	rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
 	if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
 	     !is_idle_task(current)) ||
@@ -7122,7 +7128,7 @@ void __might_sleep(const char *file, int
 #endif
 	dump_stack();
 }
-EXPORT_SYMBOL(__might_sleep);
+EXPORT_SYMBOL(___might_sleep);
 #endif
 
 #ifdef CONFIG_MAGIC_SYSRQ

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