kmemleak: Allow the early log buffer to be configurable.

(feature suggested by Sergey Senozhatsky)

Kmemleak needs to track all the memory allocations but some of these
happen before kmemleak is initialised. These are stored in an internal
buffer which may be exceeded in some kernel configurations. This patch
adds a configuration option with a default value of 400 and also removes
the stack dump when the early log buffer is exceeded.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by>

Documentation/kmemleak.txt

@@ -41,6 +41,10 @@ Memory scanning parameters can be modified at run-time by writing to the
 Kmemleak can also be disabled at boot-time by passing "kmemleak=off" on
 the kernel command line.
 
+Memory may be allocated or freed before kmemleak is initialised and
+these actions are stored in an early log buffer. The size of this buffer
+is configured via the CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE option.
+
 Basic Algorithm
 ---------------
 

lib/Kconfig.debug

@@ -359,6 +359,18 @@ config DEBUG_KMEMLEAK
 	  In order to access the kmemleak file, debugfs needs to be
 	  mounted (usually at /sys/kernel/debug).
 
+config DEBUG_KMEMLEAK_EARLY_LOG_SIZE
+	int "Maximum kmemleak early log entries"
+	depends on DEBUG_KMEMLEAK
+	range 200 2000
+	default 400
+	help
+	  Kmemleak must track all the memory allocations to avoid
+	  reporting false positives. Since memory may be allocated or
+	  freed before kmemleak is initialised, an early log buffer is
+	  used to store these actions. If kmemleak reports "early log
+	  buffer exceeded", please increase this value.
+
 config DEBUG_KMEMLEAK_TEST
 	tristate "Simple test for the kernel memory leak detector"
 	depends on DEBUG_KMEMLEAK

mm/kmemleak.c

@@ -235,7 +235,7 @@ struct early_log {
 };
 
 /* early logging buffer and current position */
-static struct early_log early_log[200];
+static struct early_log early_log[CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE];
 static int crt_early_log;
 
 static void kmemleak_disable(void);
@@ -696,7 +696,8 @@ static void log_early(int op_type, const void *ptr, size_t size,
 	struct early_log *log;
 
 	if (crt_early_log >= ARRAY_SIZE(early_log)) {
-		kmemleak_stop("Early log buffer exceeded\n");
+		pr_warning("Early log buffer exceeded\n");
+		kmemleak_disable();
 		return;
 	}