ext4: mballoc: make mb_debug() implementation to use pr_debug()

mb_debug() msg had only 1 control level for all type of msgs.
And if we enable mballoc_debug then all of those msgs would be enabled.
Instead of adding multiple debug levels for mb_debug() msgs, use
pr_debug() with which we could have finer control to print msgs at all
of different levels (i.e. at file, func, line no.).

Also add process name/pid, superblk id, and other info in mb_debug()
msg. This also kills the mballoc_debug module parameter, since it is
not needed any more.
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/f0c660cbde9e2edbe95c67942ca9ad80dd2231eb.1589086800.git.riteshh@linux.ibm.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/Kconfig

@@ -99,8 +99,7 @@ config EXT4_DEBUG
 	  Enables run-time debugging support for the ext4 filesystem.
 
 	  If you select Y here, then you will be able to turn on debugging
-	  with a command such as:
-		echo 1 > /sys/module/ext4/parameters/mballoc_debug
+	  using dynamic debug control for mb_debug() msgs.
 
 config EXT4_KUNIT_TESTS
 	tristate "KUnit tests for ext4"

fs/ext4/mballoc.h

@@ -24,19 +24,15 @@
 #include "ext4.h"
 
 /*
+ * mb_debug() dynamic printk msgs could be used to debug mballoc code.
  */
 #ifdef CONFIG_EXT4_DEBUG
-extern ushort ext4_mballoc_debug;
-
-#define mb_debug(n, fmt, ...)	                                        \
-do {									\
-	if ((n) <= ext4_mballoc_debug) {				\
-		printk(KERN_DEBUG "(%s, %d): %s: " fmt,			\
-		       __FILE__, __LINE__, __func__, ##__VA_ARGS__);	\
-	}								\
-} while (0)
+#define mb_debug(sb, fmt, ...)						\
+	pr_debug("[%s/%d] EXT4-fs (%s): (%s, %d): %s: " fmt,		\
+		current->comm, task_pid_nr(current), sb->s_id,		\
+	       __FILE__, __LINE__, __func__, ##__VA_ARGS__)
 #else
-#define mb_debug(n, fmt, ...)	no_printk(fmt, ##__VA_ARGS__)
+#define mb_debug(sb, fmt, ...)	no_printk(fmt, ##__VA_ARGS__)
 #endif
 
 #define EXT4_MB_HISTORY_ALLOC		1	/* allocation */