[PATCH] kmemleak: Add option to print warnings to dmesg

[PATCH] kmemleak: Add option to print warnings to dmesg

[Vincent Whitchurch]

Currently, kmemleak only prints the number of suspected leaks to dmesg
but requires the user to read a debugfs file to get the actual stack
traces of the objects' allocation points.  Add an option to print the
stack trace information (except the hex dumps) to dmesg too.  This
allows easier integration of kmemleak into automated test systems since
those kind of systems presumably already save kernel logs.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
---
 lib/Kconfig.debug |  9 +++++++++
 mm/kmemleak.c     | 21 +++++++++++++++++----
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ab1b599202bc..9a3fc905b8bd 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -593,6 +593,15 @@ config DEBUG_KMEMLEAK_DEFAULT_OFF
 	  Say Y here to disable kmemleak by default. It can then be enabled
 	  on the command line via kmemleak=on.
 
+config DEBUG_KMEMLEAK_WARN
+	bool "Print kmemleak object warnings to log buffer"
+	depends on DEBUG_KMEMLEAK
+	help
+	  Say Y here to make kmemleak print information about unreferenced
+	  objects (including stacktraces) as warnings to the kernel log buffer.
+	  Otherwise this information is only available by reading the kmemleak
+	  debugfs file.
+
 config DEBUG_STACK_USAGE
 	bool "Stack utilization instrumentation"
 	depends on DEBUG_KERNEL && !IA64
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 9a085d525bbc..61ba47a357fc 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -311,6 +311,9 @@ static void hex_dump_object(struct seq_file *seq,
 	const u8 *ptr = (const u8 *)object->pointer;
 	size_t len;
 
+	if (!seq)
+		return;
+
 	/* limit the number of lines to HEX_MAX_LINES */
 	len = min_t(size_t, object->size, HEX_MAX_LINES * HEX_ROW_SIZE);
 
@@ -355,6 +358,13 @@ static bool unreferenced_object(struct kmemleak_object *object)
 			       jiffies_last_scan);
 }
 
+#define warn_or_seq_printf(seq, fmt, ...)	do {	\
+	if (seq)					\
+		seq_printf(seq, fmt, ##__VA_ARGS__);	\
+	else						\
+		pr_warn(fmt, ##__VA_ARGS__);		\
+} while (0)
+
 /*
  * Printing of the unreferenced objects information to the seq file. The
  * print_unreferenced function must be called with the object->lock held.
@@ -365,17 +375,17 @@ static void print_unreferenced(struct seq_file *seq,
 	int i;
 	unsigned int msecs_age = jiffies_to_msecs(jiffies - object->jiffies);
 
-	seq_printf(seq, "unreferenced object 0x%08lx (size %zu):\n",
+	warn_or_seq_printf(seq, "unreferenced object 0x%08lx (size %zu):\n",
 		   object->pointer, object->size);
-	seq_printf(seq, "  comm \"%s\", pid %d, jiffies %lu (age %d.%03ds)\n",
+	warn_or_seq_printf(seq, "  comm \"%s\", pid %d, jiffies %lu (age %d.%03ds)\n",
 		   object->comm, object->pid, object->jiffies,
 		   msecs_age / 1000, msecs_age % 1000);
 	hex_dump_object(seq, object);
-	seq_printf(seq, "  backtrace:\n");
+	warn_or_seq_printf(seq, "  backtrace:\n");
 
 	for (i = 0; i < object->trace_len; i++) {
 		void *ptr = (void *)object->trace[i];
-		seq_printf(seq, "    [<%p>] %pS\n", ptr, ptr);
+		warn_or_seq_printf(seq, "    [<%p>] %pS\n", ptr, ptr);
 	}
 }
 
@@ -1598,6 +1608,9 @@ static void kmemleak_scan(void)
 		if (unreferenced_object(object) &&
 		    !(object->flags & OBJECT_REPORTED)) {
 			object->flags |= OBJECT_REPORTED;
+#ifdef CONFIG_DEBUG_KMEMLEAK_WARN
+			print_unreferenced(NULL, object);
+#endif
 			new_leaks++;
 		}
 		spin_unlock_irqrestore(&object->lock, flags);
-- 
2.11.0

Re: [PATCH] kmemleak: Add option to print warnings to dmesg

[Catalin Marinas]

On Fri, Aug 24, 2018 at 02:40:11PM +0200, Vincent Whitchurch wrote:
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 9a085d525bbc..61ba47a357fc 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -311,6 +311,9 @@ static void hex_dump_object(struct seq_file *seq,
>  	const u8 *ptr = (const u8 *)object->pointer;
>  	size_t len;
>  
> +	if (!seq)
> +		return;
> +
>  	/* limit the number of lines to HEX_MAX_LINES */
>  	len = min_t(size_t, object->size, HEX_MAX_LINES * HEX_ROW_SIZE);
>  

We have a print_hex_dump() function you could use here instead of
skipping it. Sometimes such information is useful to capture part of the
object state.

-- 
Catalin