[PATCH] ext4: convert legacy ext4_debug() to standard pr_debug()

[lirongqing <lirongqing@baidu.com>]

From: Li RongQing <lirongqing@baidu.com>

The ext4 file system historically implemented its own debug logging macro
ext4_debug() via EXT4FS_DEBUG conditional compilation. This legacy
implementation suffers from two major drawbacks:

1. It makes two consecutive un-serialized printk() calls, which can
   lead to severe log interleaving and corruption under multi-core
   concurrent workloads.
2. It completely bypasses the standard modern kernel dynamic debug
   (CONFIG_DYNAMIC_DEBUG) infrastructure.

Clean up the legacy implementation by leveraging pr_debug(). This squashes
the multiple printk() calls into a single atomic execution, ensuring
log integrity, while seamlessly hooking ext4 into the kernel's native
dynamic debug framework.

The redundant __FILE__ and __LINE__ macros are intentionally removed from
the string format because the dynamic debug infrastructure can already
append them automatically at runtime (via the '+fl' flags) if desired.
This avoids redundancy and double-logging in modern production/debugging
environments while keeping the macro clean and robust against dangling
comma compiler errors.

Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
 fs/ext4/ext4.h | 20 ++------------------
 1 file changed, 2 insertions(+), 18 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 94283a9..39e86ff 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -62,24 +62,8 @@
  */
 #define DOUBLE_CHECK__
 
-/*
- * Define EXT4FS_DEBUG to produce debug messages
- */
-#undef EXT4FS_DEBUG
-
-/*
- * Debug code
- */
-#ifdef EXT4FS_DEBUG
-#define ext4_debug(f, a...)						\
-	do {								\
-		printk(KERN_DEBUG "EXT4-fs DEBUG (%s, %d): %s:",	\
-			__FILE__, __LINE__, __func__);			\
-		printk(KERN_DEBUG f, ## a);				\
-	} while (0)
-#else
-#define ext4_debug(fmt, ...)	no_printk(fmt, ##__VA_ARGS__)
-#endif
+#define ext4_debug(fmt, ...)						\
+	pr_debug("EXT4-fs DEBUG %s: " fmt, __func__,  ##__VA_ARGS__)
 
  /*
   * Turn on EXT_DEBUG to enable ext4_ext_show_path/leaf/move in extents.c
-- 
2.9.4