linux-kernel - Re: odd lockdep messages

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Date:	Tue, 09 Mar 2010 10:54:20 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Valdis.Kletnieks@...edu, Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: odd lockdep messages

On 03/09/2010 03:43 AM, Peter Zijlstra wrote:
>> [    1.899537] BUG: key ffff88011c57e670 not in .data!
>>
>> (-0302 threw BUG: 3 times, the first 2 and the last. In -0304, the third
>> one appears as well).
>>
>> Worth instrumenting and chasing down? If so, what should a crash test dummy
>> be doing here? ;)
> 
> Can that be wreckage due to the new per-cpu stuff?
> 
> Its a message printed when the below function fails, and that per-cpu
> stuff seems the one most likely to break, given that there was quite a
> lot of churn in that department recently.

Yeap, PERCPU_ENOUGH_ROOM test doesn't hold anymore.  Does the
following patch fix the problem?

Thanks.

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index a93e5bf..6d300f5 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -137,6 +137,7 @@ extern int __init pcpu_page_first_chunk(size_t reserved_size,
 extern void __percpu *__alloc_reserved_percpu(size_t size, size_t align);
 extern void __percpu *__alloc_percpu(size_t size, size_t align);
 extern void free_percpu(void __percpu *__pdata);
+extern bool is_static_percpu_address(unsigned long addr);
 extern phys_addr_t per_cpu_ptr_to_phys(void *addr);
 
 #ifndef CONFIG_HAVE_SETUP_PER_CPU_AREA
@@ -163,6 +164,12 @@ static inline void free_percpu(void __percpu *p)
 	kfree(p);
 }
 
+/* can't distinguish from other static vars, always %false */
+static inline bool is_static_percpu_address(unsigned long addr)
+{
+	return false;
+}
+
 static inline phys_addr_t per_cpu_ptr_to_phys(void *addr)
 {
 	return __pa(addr);
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 0c30d04..4206f6f 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -582,9 +582,6 @@ static int static_obj(void *obj)
 	unsigned long start = (unsigned long) &_stext,
 		      end   = (unsigned long) &_end,
 		      addr  = (unsigned long) obj;
-#ifdef CONFIG_SMP
-	int i;
-#endif
 
 	/*
 	 * static variable?
@@ -595,19 +592,11 @@ static int static_obj(void *obj)
 	if (arch_is_kernel_data(addr))
 		return 1;
 
-#ifdef CONFIG_SMP
 	/*
 	 * percpu var?
 	 */
-	for_each_possible_cpu(i) {
-		start = (unsigned long) &__per_cpu_start + per_cpu_offset(i);
-		end   = (unsigned long) &__per_cpu_start + PERCPU_ENOUGH_ROOM
-					+ per_cpu_offset(i);
-
-		if ((addr >= start) && (addr < end))
-			return 1;
-	}
-#endif
+	if (is_static_percpu_address(addr))
+		return 1;
 
 	/*
 	 * module var?
diff --git a/mm/percpu.c b/mm/percpu.c
index 768419d..ae4d058 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1304,6 +1304,32 @@ void free_percpu(void __percpu *ptr)
 EXPORT_SYMBOL_GPL(free_percpu);
 
 /**
+ * is_static_percpu_address - test whether address is from static percpu area
+ * @addr: address to test
+ *
+ * Test whether @addr belongs to static percpu area.  Module static
+ * percpu areas allocated via __alloc_reserved_percpu() is not
+ * considered.  Use is_module_address() for those.
+ *
+ * RETURNS:
+ * %true if @addr is from static percpu area, %false otherwise.
+ */
+bool is_static_percpu_address(unsigned long addr)
+{
+	const size_t static_size = __per_cpu_end - __per_cpu_start;
+	void __percpu *base = __addr_to_pcpu_ptr(pcpu_base_addr);
+	unsigned int cpu;
+
+	for_each_possible_cpu(cpu) {
+		void *start = per_cpu_ptr(base, cpu);
+
+		if ((void *)addr >= start && (void *)addr < start + static_size)
+			return true;
+        }
+	return false;
+}
+
+/**
  * per_cpu_ptr_to_phys - convert translated percpu address to physical address
  * @addr: the address to be converted to physical address
  *

-- 
tejun
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