[PATCH v2 1/3] kmemleak: allow freeing internal objects after kmemleak was disabled

[PATCH v2 1/3] kmemleak: allow freeing internal objects after kmemleak was disabled

[Li Zefan]

Currently if kmemleak is disabled, the kmemleak objects can never be freed,
no matter if it's disabled by a user or due to fatal errors.

Those objects can be a big waste of memory.

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
1200264 1197433  99%    0.30K  46164       26    369312K kmemleak_object

With this patch, internal objects will be freed immediately if kmemleak is
disabled explicitly by a user. If it's disabled due to a kmemleak error,
The user will be informed, and then he/she can reclaim memory with:

	# echo off > /sys/kernel/debug/kmemleak

v2: use "off" handler instead of "clear" handler to do this, suggested
    by Catalin.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 Documentation/kmemleak.txt | 14 +++++++++++++-
 mm/kmemleak.c              | 21 ++++++++++++++++-----
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/Documentation/kmemleak.txt b/Documentation/kmemleak.txt
index 6dc8013..00aa013 100644
--- a/Documentation/kmemleak.txt
+++ b/Documentation/kmemleak.txt
@@ -42,7 +42,8 @@ objects to be reported as orphan.
 Memory scanning parameters can be modified at run-time by writing to the
 /sys/kernel/debug/kmemleak file. The following parameters are supported:
 
-  off		- disable kmemleak (irreversible)
+  off		- disable kmemleak, or free all kmemleak objects if kmemleak
+		  has been disabled due to fatal errors. (irreversible).
   stack=on	- enable the task stacks scanning (default)
   stack=off	- disable the tasks stacks scanning
   scan=on	- start the automatic memory scanning thread (default)
@@ -118,6 +119,17 @@ Then as usual to get your report with:
 
   # cat /sys/kernel/debug/kmemleak
 
+Freeing kmemleak internal objects
+---------------------------------
+
+To allow access to previously found memory leaks even when an error fatal
+to kmemleak happens, internal kmemleak objects won't be freed in this case.
+Those objects may occupy a large part of physical memory.
+
+You can reclaim memory from those objects with:
+
+  # echo off > /sys/kernel/debug/kmemleak
+
 Kmemleak API
 ------------
 
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 31f01c5..7fc030e 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1616,9 +1616,6 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
 	int buf_size;
 	int ret;
 
-	if (!atomic_read(&kmemleak_enabled))
-		return -EBUSY;
-
 	buf_size = min(size, (sizeof(buf) - 1));
 	if (strncpy_from_user(buf, user_buf, buf_size) < 0)
 		return -EFAULT;
@@ -1628,9 +1625,18 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
 	if (ret < 0)
 		return ret;
 
-	if (strncmp(buf, "off", 3) == 0)
+	if (strncmp(buf, "off", 3) == 0) {
+		stop_scan_thread();
 		kmemleak_disable();
-	else if (strncmp(buf, "stack=on", 8) == 0)
+		goto out;
+	}
+
+	if (!atomic_read(&kmemleak_enabled)) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	if (strncmp(buf, "stack=on", 8) == 0)
 		kmemleak_stack_scan = 1;
 	else if (strncmp(buf, "stack=off", 9) == 0)
 		kmemleak_stack_scan = 0;
@@ -1695,6 +1701,11 @@ static void kmemleak_do_cleanup(struct work_struct *work)
 		list_for_each_entry_rcu(object, &object_list, object_list)
 			delete_object_full(object->pointer);
 		rcu_read_unlock();
+	} else {
+		pr_info("Disable kmemleak without freeing internal objects, "
+			"so you may still check information on memory leak. "
+			"You may reclaim memory by writing \"off\" to "
+			"/sys/kernel/debug/kmemleak\n");
 	}
 	mutex_unlock(&scan_mutex);
 }
-- 
1.8.0.2

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[PATCH v2 2/3] kmemleak: remove redundant code

[Li Zefan]

- remove kmemleak_padding().
- remove kmemleak_release().

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 include/linux/kmemleak.h | 2 --
 mm/kmemleak.c            | 7 +------
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/include/linux/kmemleak.h b/include/linux/kmemleak.h
index 2a5e554..5bb4246 100644
--- a/include/linux/kmemleak.h
+++ b/include/linux/kmemleak.h
@@ -30,8 +30,6 @@ extern void kmemleak_alloc_percpu(const void __percpu *ptr, size_t size) __ref;
 extern void kmemleak_free(const void *ptr) __ref;
 extern void kmemleak_free_part(const void *ptr, size_t size) __ref;
 extern void kmemleak_free_percpu(const void __percpu *ptr) __ref;
-extern void kmemleak_padding(const void *ptr, unsigned long offset,
-			     size_t size) __ref;
 extern void kmemleak_not_leak(const void *ptr) __ref;
 extern void kmemleak_ignore(const void *ptr) __ref;
 extern void kmemleak_scan_area(const void *ptr, size_t size, gfp_t gfp) __ref;
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 7fc030e..54270f2 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1545,11 +1545,6 @@ static int kmemleak_open(struct inode *inode, struct file *file)
 	return seq_open(file, &kmemleak_seq_ops);
 }
 
-static int kmemleak_release(struct inode *inode, struct file *file)
-{
-	return seq_release(inode, file);
-}
-
 static int dump_str_object_info(const char *str)
 {
 	unsigned long flags;
@@ -1680,7 +1675,7 @@ static const struct file_operations kmemleak_fops = {
 	.read		= seq_read,
 	.write		= kmemleak_write,
 	.llseek		= seq_lseek,
-	.release	= kmemleak_release,
+	.release	= seq_release,
 };
 
 /*
-- 
1.8.0.2

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[PATCH v2 3/3] kmemleak: change some global variables to int

[Li Zefan]

They don't have to be atomic_t, because they are simple boolean
toggles.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 mm/kmemleak.c | 78 +++++++++++++++++++++++++++++------------------------------
 1 file changed, 39 insertions(+), 39 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 54270f2..c352c63 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -192,15 +192,15 @@ static struct kmem_cache *object_cache;
 static struct kmem_cache *scan_area_cache;
 
 /* set if tracing memory operations is enabled */
-static atomic_t kmemleak_enabled = ATOMIC_INIT(0);
+static int kmemleak_enabled;
 /* set in the late_initcall if there were no errors */
-static atomic_t kmemleak_initialized = ATOMIC_INIT(0);
+static int kmemleak_initialized;
 /* enables or disables early logging of the memory operations */
-static atomic_t kmemleak_early_log = ATOMIC_INIT(1);
+static int kmemleak_early_log = 1;
 /* set if a kmemleak warning was issued */
-static atomic_t kmemleak_warning = ATOMIC_INIT(0);
+static int kmemleak_warning;
 /* set if a fatal kmemleak error has occurred */
-static atomic_t kmemleak_error = ATOMIC_INIT(0);
+static int kmemleak_error;
 
 /* minimum and maximum address that may be valid pointers */
 static unsigned long min_addr = ULONG_MAX;
@@ -267,7 +267,7 @@ static void kmemleak_disable(void);
 #define kmemleak_warn(x...)	do {		\
 	pr_warning(x);				\
 	dump_stack();				\
-	atomic_set(&kmemleak_warning, 1);	\
+	kmemleak_warning = 1;			\
 } while (0)
 
 /*
@@ -805,7 +805,7 @@ static void __init log_early(int op_type, const void *ptr, size_t size,
 	unsigned long flags;
 	struct early_log *log;
 
-	if (atomic_read(&kmemleak_error)) {
+	if (kmemleak_error) {
 		/* kmemleak stopped recording, just count the requests */
 		crt_early_log++;
 		return;
@@ -840,7 +840,7 @@ static void early_alloc(struct early_log *log)
 	unsigned long flags;
 	int i;
 
-	if (!atomic_read(&kmemleak_enabled) || !log->ptr || IS_ERR(log->ptr))
+	if (!kmemleak_enabled || !log->ptr || IS_ERR(log->ptr))
 		return;
 
 	/*
@@ -893,9 +893,9 @@ void __ref kmemleak_alloc(const void *ptr, size_t size, int min_count,
 {
 	pr_debug("%s(0x%p, %zu, %d)\n", __func__, ptr, size, min_count);
 
-	if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
 		create_object((unsigned long)ptr, size, min_count, gfp);
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_ALLOC, ptr, size, min_count);
 }
 EXPORT_SYMBOL_GPL(kmemleak_alloc);
@@ -919,11 +919,11 @@ void __ref kmemleak_alloc_percpu(const void __percpu *ptr, size_t size)
 	 * Percpu allocations are only scanned and not reported as leaks
 	 * (min_count is set to 0).
 	 */
-	if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
 		for_each_possible_cpu(cpu)
 			create_object((unsigned long)per_cpu_ptr(ptr, cpu),
 				      size, 0, GFP_KERNEL);
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_ALLOC_PERCPU, ptr, size, 0);
 }
 EXPORT_SYMBOL_GPL(kmemleak_alloc_percpu);
@@ -939,9 +939,9 @@ void __ref kmemleak_free(const void *ptr)
 {
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
 		delete_object_full((unsigned long)ptr);
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_FREE, ptr, 0, 0);
 }
 EXPORT_SYMBOL_GPL(kmemleak_free);
@@ -959,9 +959,9 @@ void __ref kmemleak_free_part(const void *ptr, size_t size)
 {
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
 		delete_object_part((unsigned long)ptr, size);
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_FREE_PART, ptr, size, 0);
 }
 EXPORT_SYMBOL_GPL(kmemleak_free_part);
@@ -979,11 +979,11 @@ void __ref kmemleak_free_percpu(const void __percpu *ptr)
 
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
 		for_each_possible_cpu(cpu)
 			delete_object_full((unsigned long)per_cpu_ptr(ptr,
 								      cpu));
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_FREE_PERCPU, ptr, 0, 0);
 }
 EXPORT_SYMBOL_GPL(kmemleak_free_percpu);
@@ -999,9 +999,9 @@ void __ref kmemleak_not_leak(const void *ptr)
 {
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
 		make_gray_object((unsigned long)ptr);
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_NOT_LEAK, ptr, 0, 0);
 }
 EXPORT_SYMBOL(kmemleak_not_leak);
@@ -1019,9 +1019,9 @@ void __ref kmemleak_ignore(const void *ptr)
 {
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
 		make_black_object((unsigned long)ptr);
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_IGNORE, ptr, 0, 0);
 }
 EXPORT_SYMBOL(kmemleak_ignore);
@@ -1041,9 +1041,9 @@ void __ref kmemleak_scan_area(const void *ptr, size_t size, gfp_t gfp)
 {
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (atomic_read(&kmemleak_enabled) && ptr && size && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && size && !IS_ERR(ptr))
 		add_scan_area((unsigned long)ptr, size, gfp);
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_SCAN_AREA, ptr, size, 0);
 }
 EXPORT_SYMBOL(kmemleak_scan_area);
@@ -1061,9 +1061,9 @@ void __ref kmemleak_no_scan(const void *ptr)
 {
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
+	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
 		object_no_scan((unsigned long)ptr);
-	else if (atomic_read(&kmemleak_early_log))
+	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_NO_SCAN, ptr, 0, 0);
 }
 EXPORT_SYMBOL(kmemleak_no_scan);
@@ -1088,7 +1088,7 @@ static bool update_checksum(struct kmemleak_object *object)
  */
 static int scan_should_stop(void)
 {
-	if (!atomic_read(&kmemleak_enabled))
+	if (!kmemleak_enabled)
 		return 1;
 
 	/*
@@ -1626,7 +1626,7 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
 		goto out;
 	}
 
-	if (!atomic_read(&kmemleak_enabled)) {
+	if (!kmemleak_enabled) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -1714,14 +1714,14 @@ static DECLARE_WORK(cleanup_work, kmemleak_do_cleanup);
 static void kmemleak_disable(void)
 {
 	/* atomically check whether it was already invoked */
-	if (atomic_cmpxchg(&kmemleak_error, 0, 1))
+	if (cmpxchg(&kmemleak_error, 0, 1))
 		return;
 
 	/* stop any memory operation tracing */
-	atomic_set(&kmemleak_enabled, 0);
+	kmemleak_enabled = 0;
 
 	/* check whether it is too early for a kernel thread */
-	if (atomic_read(&kmemleak_initialized))
+	if (kmemleak_initialized)
 		schedule_work(&cleanup_work);
 
 	pr_info("Kernel memory leak detector disabled\n");
@@ -1763,9 +1763,10 @@ void __init kmemleak_init(void)
 	int i;
 	unsigned long flags;
 
+	kmemleak_early_log = 0;
+
 #ifdef CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF
 	if (!kmemleak_skip_disable) {
-		atomic_set(&kmemleak_early_log, 0);
 		kmemleak_disable();
 		return;
 	}
@@ -1783,12 +1784,11 @@ void __init kmemleak_init(void)
 
 	/* the kernel is still in UP mode, so disabling the IRQs is enough */
 	local_irq_save(flags);
-	atomic_set(&kmemleak_early_log, 0);
-	if (atomic_read(&kmemleak_error)) {
+	if (kmemleak_error) {
 		local_irq_restore(flags);
 		return;
 	} else
-		atomic_set(&kmemleak_enabled, 1);
+		kmemleak_enabled = 1;
 	local_irq_restore(flags);
 
 	/*
@@ -1832,9 +1832,9 @@ void __init kmemleak_init(void)
 				      log->op_type);
 		}
 
-		if (atomic_read(&kmemleak_warning)) {
+		if (kmemleak_warning) {
 			print_log_trace(log);
-			atomic_set(&kmemleak_warning, 0);
+			kmemleak_warning = 0;
 		}
 	}
 }
@@ -1846,9 +1846,9 @@ static int __init kmemleak_late_init(void)
 {
 	struct dentry *dentry;
 
-	atomic_set(&kmemleak_initialized, 1);
+	kmemleak_initialized = 1;
 
-	if (atomic_read(&kmemleak_error)) {
+	if (kmemleak_error) {
 		/*
 		 * Some error occurred and kmemleak was disabled. There is a
 		 * small chance that kmemleak_disable() was called immediately
-- 
1.8.0.2

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Re: [PATCH v2 1/3] kmemleak: allow freeing internal objects after kmemleak was disabled

[Catalin Marinas]

Hi Li,

On 17 Mar 2014, at 04:07, Li Zefan <lizefan@huawei.com> wrote:
> Currently if kmemleak is disabled, the kmemleak objects can never be freed,
> no matter if it's disabled by a user or due to fatal errors.
> 
> Those objects can be a big waste of memory.
> 
>  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
> 1200264 1197433  99%    0.30K  46164       26    369312K kmemleak_object
> 
> With this patch, internal objects will be freed immediately if kmemleak is
> disabled explicitly by a user. If it's disabled due to a kmemleak error,
> The user will be informed, and then he/she can reclaim memory with:
> 
> 	# echo off > /sys/kernel/debug/kmemleak
> 
> v2: use "off" handler instead of "clear" handler to do this, suggested
>    by Catalin.

I think there was a slight misunderstanding. My point was about "echo
scan=off” before “echo off”, they can just be squashed into the
same action of the latter.

I would keep the “clear” part separately as per your first patch. I
recall people asked in the past to still be able to analyse the reports
even though kmemleak failed or was disabled.

Thanks,

Catalin
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Re: [PATCH v2 2/3] kmemleak: remove redundant code

[Catalin Marinas]

On Mon, Mar 17, 2014 at 04:08:00AM +0000, Li Zefan wrote:
> - remove kmemleak_padding().
> - remove kmemleak_release().
> 
> Signed-off-by: Li Zefan <lizefan@huawei.com>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

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Re: [PATCH v2 3/3] kmemleak: change some global variables to int

[Catalin Marinas]

On Mon, Mar 17, 2014 at 04:09:04AM +0000, Li Zefan wrote:
> They don't have to be atomic_t, because they are simple boolean
> toggles.
> 
> Signed-off-by: Li Zefan <lizefan@huawei.com>

A reason for which I had atomic_t was to avoid compiler optimisations
but I don't immediately see how it could go wrong. Assuming that you
have tested it,

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

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Re: [PATCH v2 1/3] kmemleak: allow freeing internal objects after kmemleak was disabled

[Li Zefan]

(Just came back from travelling)

On 2014/3/22 7:37, Catalin Marinas wrote:
> Hi Li,
> 
> On 17 Mar 2014, at 04:07, Li Zefan <lizefan@huawei.com> wrote:
>> Currently if kmemleak is disabled, the kmemleak objects can never be freed,
>> no matter if it's disabled by a user or due to fatal errors.
>>
>> Those objects can be a big waste of memory.
>>
>>  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
>> 1200264 1197433  99%    0.30K  46164       26    369312K kmemleak_object
>>
>> With this patch, internal objects will be freed immediately if kmemleak is
>> disabled explicitly by a user. If it's disabled due to a kmemleak error,
>> The user will be informed, and then he/she can reclaim memory with:
>>
>> 	# echo off > /sys/kernel/debug/kmemleak
>>
>> v2: use "off" handler instead of "clear" handler to do this, suggested
>>    by Catalin.
> 
> I think there was a slight misunderstanding. My point was about "echo
> scan=off!+- before !?echo off!+-, they can just be squashed into the
> same action of the latter.
> 

I'm not sure if I understand correctly, so you want the "off" handler to
stop the scan thread but it will never free kmemleak objects until the 
user explicitly trigger the "clear" action, right?

> I would keep the !?clear!+- part separately as per your first patch. I
> recall people asked in the past to still be able to analyse the reports
> even though kmemleak failed or was disabled.
> 

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Re: [PATCH v2 1/3] kmemleak: allow freeing internal objects after kmemleak was disabled

[Catalin Marinas]

On Thu, Mar 27, 2014 at 02:29:18AM +0000, Li Zefan wrote:
> On 2014/3/22 7:37, Catalin Marinas wrote:
> > On 17 Mar 2014, at 04:07, Li Zefan <lizefan@huawei.com> wrote:
> >> Currently if kmemleak is disabled, the kmemleak objects can never be freed,
> >> no matter if it's disabled by a user or due to fatal errors.
> >>
> >> Those objects can be a big waste of memory.
> >>
> >>  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
> >> 1200264 1197433  99%    0.30K  46164       26    369312K kmemleak_object
> >>
> >> With this patch, internal objects will be freed immediately if kmemleak is
> >> disabled explicitly by a user. If it's disabled due to a kmemleak error,
> >> The user will be informed, and then he/she can reclaim memory with:
> >>
> >> 	# echo off > /sys/kernel/debug/kmemleak
> >>
> >> v2: use "off" handler instead of "clear" handler to do this, suggested
> >>    by Catalin.
> > 
> > I think there was a slight misunderstanding. My point was about "echo
> > scan=offa?? before a??echo offa??, they can just be squashed into the
> > same action of the latter.
> 
> I'm not sure if I understand correctly, so you want the "off" handler to
> stop the scan thread but it will never free kmemleak objects until the 
> user explicitly trigger the "clear" action, right?

Yes. That's just in case someone wants to stop kmemleak but still
investigate some previously reported leaks.

Thanks.

-- 
Catalin

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