[PATCH] Buffer-layer tracing support for jbd/jbd2 related repo: https://github.com/huwan/linux-buffer-debug

Buffer-layer tracing support for ext4-jbd2.patch

From 279cb88d74c75e5dc4876a2dcd1f1aefc62d60ba Mon Sep 17 00:00:00 2001
From: Wan Hu <wanhu@cnu.edu.cn>
Date: Thu, 3 Sep 2015 20:41:09 +0800
Subject: [PATCH] Buffer-layer tracing support for ext4/jbd2

---
 fs/Kconfig                   |   4 +
 fs/Makefile                  |   1 +
 fs/jbd2-kernel.c             | 254 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/buffer-trace.h |  52 +++++++++
 include/linux/buffer_head.h  |   6 +-
 include/linux/config.h       |   8 ++
 include/linux/jbd.h          |   2 +-
 include/linux/jbd2.h         |  30 +++++
 8 files changed, 355 insertions(+), 2 deletions(-)
 create mode 100644 fs/jbd2-kernel.c
 create mode 100644 include/linux/buffer-trace.h
 create mode 100644 include/linux/config.h

diff --git a/fs/Kconfig b/fs/Kconfig
index 64d44ef..a4e21ed 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -19,6 +19,10 @@ config FS_XIP
 source "fs/jbd/Kconfig"
 source "fs/jbd2/Kconfig"
 
+config BUFFER_DEBUG
+	bool "buffer-layer tracing"
+	depends on JBD2
+
 config FS_MBCACHE
 # Meta block cache for Extended Attributes (ext2/ext3/ext4)
 	tristate
diff --git a/fs/Makefile b/fs/Makefile
index af6d047..3e42bb7 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -36,6 +36,7 @@ obj-y				+= $(nfsd-y) $(nfsd-m)
 obj-$(CONFIG_BINFMT_AOUT)	+= binfmt_aout.o
 obj-$(CONFIG_BINFMT_EM86)	+= binfmt_em86.o
 obj-$(CONFIG_BINFMT_MISC)	+= binfmt_misc.o
+obj-$(CONFIG_BUFFER_DEBUG)	+= jbd2-kernel.o
 
 # binfmt_script is always there
 obj-y				+= binfmt_script.o
diff --git a/fs/jbd2-kernel.c b/fs/jbd2-kernel.c
new file mode 100644
index 0000000..ffb224c
--- /dev/null
+++ b/fs/jbd2-kernel.c
@@ -0,0 +1,254 @@
+/*
+ * fs/jbd2/jbd2-kernel.c
+ *
+ * Support code for the Journalling Block Device layer.
+ * This file contains things which have to be in-kernel when
+ * JBD2 is a module.
+ *
+ * 15 May 2001	Andrew Morton <andrewm@xxxxxxxxxx>
+ *	Created
+ */
+
+#include <linux/config.h>
+#include <linux/fs.h>
+#include <linux/jbd2.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+
+/*
+ * Some sanity testing which is called from mark_buffer_clean(),
+ * and must be present in the main kernel.
+ */
+
+void jbd_preclean_buffer_check(struct buffer_head *bh)
+{
+	if (buffer_jbd(bh)) {
+	struct journal_head *jh = bh2jh(bh);
+
+	transaction_t *transaction = jh->b_transaction;
+	journal_t *journal;
+
+	if (jh->b_jlist == 0 && transaction == NULL)
+	return;
+
+	J_ASSERT_JH(jh, transaction != NULL);
+	/* The kernel may be unmapping old data. We expect it
+	* to be dirty in that case, unless the buffer has
+	* already been forgotten by a transaction. */
+	if (jh->b_jlist != BJ_Forget) {
+#if 1
+	if (!buffer_dirty(bh)) {
+	printk("%s: clean of clean buffer\n",
+	__FUNCTION__);
+	print_buffer_trace(bh);
+	return;
+	}
+#endif
+	J_ASSERT_BH(bh, buffer_dirty(bh));
+	}
+
+	journal = transaction->t_journal;
+	J_ASSERT_JH(jh,
+	transaction == journal->j_running_transaction ||
+	transaction == journal->j_committing_transaction);
+	}
+}
+EXPORT_SYMBOL(jbd_preclean_buffer_check);
+
+/*
+ * Support functions for BUFFER_TRACE()
+ */
+
+static spinlock_t trace_lock = SPIN_LOCK_UNLOCKED;
+
+void buffer_trace(const char *function, struct buffer_head *dest,
+	struct buffer_head *src, char *info)
+{
+	struct buffer_history_item *bhist_i;
+	struct page *page;
+	unsigned long flags;
+
+	if (dest == 0 || src == 0)
+	return;
+
+	spin_lock_irqsave(&trace_lock, flags);
+
+	/*
+	* Sometimes we don't initialise the ring pointers. (locally declared
+	* temp buffer_heads). Feebly attempt to detect and correct that here.
+	*/
+	if ((dest->b_history.b_history_head - dest->b_history.b_history_tail >
+	BUFFER_HISTORY_SIZE)) {
+	dest->b_history.b_history_head = 0;
+	dest->b_history.b_history_tail = 0;
+	}
+	bhist_i = dest->b_history.b +
+	(dest->b_history.b_history_head & (BUFFER_HISTORY_SIZE - 1));
+	bhist_i->function = function;
+	bhist_i->info = info;
+	bhist_i->b_state = src->b_state;
+	page = src->b_page;
+	if (page)
+	bhist_i->pg_dirty = !!PageDirty(page);
+	else
+	bhist_i->pg_dirty = 0;
+
+#if defined(CONFIG_JBD2) || defined(CONFIG_JBD2_MODULE)
+	bhist_i->b_trans_is_running = 0;
+	bhist_i->b_trans_is_committing = 0;
+	bhist_i->b_blocknr = src->b_blocknr;
+	if (buffer_jbd(src)) {
+	struct journal_head *jh;
+	journal_t *journal;
+	transaction_t *transaction;
+
+	/* Footwork to avoid racing with journal_remove_journal_head */
+	jh = src->b_private;
+	if (jh == 0)
+	goto raced;
+	transaction = jh->b_transaction;
+	if (src->b_private == 0)
+	goto raced;
+	bhist_i->b_jcount = jh->b_jcount;
+	bhist_i->b_jbd = 1;
+	bhist_i->b_jlist = jh->b_jlist;
+	bhist_i->b_frozen_data = jh->b_frozen_data;
+	bhist_i->b_committed_data = jh->b_committed_data;
+	bhist_i->b_transaction = !!jh->b_transaction;
+	bhist_i->b_next_transaction = !!jh->b_next_transaction;
+	bhist_i->b_cp_transaction = !!jh->b_cp_transaction;
+
+	if (transaction) {
+	journal = transaction->t_journal;
+	bhist_i->b_trans_is_running = transaction ==
+	journal->j_running_transaction;
+	bhist_i->b_trans_is_committing = transaction ==
+	journal->j_committing_transaction;
+	}
+	} else {
+raced:
+	bhist_i->b_jcount = 0;
+	bhist_i->b_jbd = 0;
+	bhist_i->b_jlist = 0;
+	bhist_i->b_frozen_data = 0;
+	bhist_i->b_committed_data = 0;
+	bhist_i->b_transaction = 0;
+	bhist_i->b_next_transaction = 0;
+	bhist_i->b_cp_transaction = 0;
+	}
+#endif	/* defined(CONFIG_JBD2) || defined(CONFIG_JBD2_MODULE) */
+
+	bhist_i->cpu = smp_processor_id();
+	bhist_i->b_count = atomic_read(&src->b_count);
+
+	dest->b_history.b_history_head++;
+	if (dest->b_history.b_history_head - dest->b_history.b_history_tail >
+	BUFFER_HISTORY_SIZE)
+	dest->b_history.b_history_tail =
+	dest->b_history.b_history_head - BUFFER_HISTORY_SIZE;
+
+	spin_unlock_irqrestore(&trace_lock, flags);
+}
+
+static const char *b_jlist_to_string(unsigned int b_list)
+{
+	switch (b_list) {
+#if defined(CONFIG_JBD2) || defined(CONFIG_JBD2_MODULE)
+	case BJ_None:	return "BJ_None";
+	case BJ_Metadata:	return "BJ_Metadata";
+	case BJ_Forget:	return "BJ_Forget";
+	case BJ_IO:	return "BJ_IO";
+	case BJ_Shadow:	return "BJ_Shadow";
+	case BJ_LogCtl:	return "BJ_LogCtl";
+	case BJ_Reserved:	return "BJ_Reserved";
+#endif
+	default:	return "Bad b_jlist";
+	}
+}
+
+static void print_one_hist(struct buffer_history_item *bhist_i)
+{
+	printk(" %s():%s\n", bhist_i->function, bhist_i->info);
+	printk(" b_state:0x%lx b_jlist:%s cpu:%d b_count:%d b_blocknr:%lu\n",
+	bhist_i->b_state,
+	b_jlist_to_string(bhist_i->b_jlist),
+	bhist_i->cpu,
+	bhist_i->b_count,
+	bhist_i->b_blocknr);
+#if defined(CONFIG_JBD2) || defined(CONFIG_JBD2_MODULE)
+	printk(" b_jbd:%u b_frozen_data:%p b_committed_data:%p\n",
+	bhist_i->b_jbd,
+	bhist_i->b_frozen_data,
+	bhist_i->b_committed_data);
+	printk(" b_transaction:%u b_next_transaction:%u "
+	"b_cp_transaction:%u b_trans_is_running:%u\n",
+	bhist_i->b_transaction,
+	bhist_i->b_next_transaction,
+	bhist_i->b_cp_transaction,
+	bhist_i->b_trans_is_running);
+	printk(" b_trans_is_comitting:%u b_jcount:%u pg_dirty:%u",
+	bhist_i->b_trans_is_committing,
+	bhist_i->b_jcount,
+	bhist_i->pg_dirty);
+#endif
+	printk("\n");
+}
+
+void print_buffer_fields(struct buffer_head *bh)
+{
+	printk("b_blocknr:%llu b_count:%d\n",
+	(unsigned long long)bh->b_blocknr, atomic_read(&bh->b_count));
+	printk("b_this_page:%p b_data:%p b_page:%p\n",
+	bh->b_this_page, bh->b_data, bh->b_page);
+#if defined(CONFIG_JBD2) || defined(CONFIG_JBD2_MODULE)
+	if (buffer_jbd(bh)) {
+	struct journal_head *jh = bh2jh(bh);
+
+	printk("b_jlist:%u b_frozen_data:%p b_committed_data:%p\n",
+	jh->b_jlist, jh->b_frozen_data, jh->b_committed_data);
+	printk(" b_transaction:%p b_next_transaction:%p "
+	"b_cp_transaction:%p\n",
+	jh->b_transaction, jh->b_next_transaction,
+	jh->b_cp_transaction);
+	printk("b_cpnext:%p b_cpprev:%p\n",
+	jh->b_cpnext, jh->b_cpprev);
+	}
+#endif
+}
+
+void print_buffer_trace(struct buffer_head *bh)
+{
+	unsigned long idx, count;
+	unsigned long flags;
+
+	printk("buffer trace for buffer at 0x%p (I am CPU %d)\n",
+	bh, smp_processor_id());
+	BUFFER_TRACE(bh, "");	/* Record state now */
+
+	spin_lock_irqsave(&trace_lock, flags);
+	for (	idx = bh->b_history.b_history_tail, count = 0;
+	idx < bh->b_history.b_history_head &&
+	count < BUFFER_HISTORY_SIZE;
+	idx++, count++)
+	print_one_hist(bh->b_history.b +
+	(idx & (BUFFER_HISTORY_SIZE - 1)));
+
+	print_buffer_fields(bh);
+	spin_unlock_irqrestore(&trace_lock, flags);
+	dump_stack();
+	printk("\n");
+}
+
+static struct buffer_head *failed_buffer_head;	/* For access with debuggers */
+
+void buffer_assertion_failure(struct buffer_head *bh)
+{
+	console_verbose();
+	failed_buffer_head = bh;
+	print_buffer_trace(bh);
+}
+EXPORT_SYMBOL(buffer_trace);
+EXPORT_SYMBOL(print_buffer_trace);
+EXPORT_SYMBOL(buffer_assertion_failure);
+EXPORT_SYMBOL(print_buffer_fields);
diff --git a/include/linux/buffer-trace.h b/include/linux/buffer-trace.h
new file mode 100644
index 0000000..39951e1
--- /dev/null
+++ b/include/linux/buffer-trace.h
@@ -0,0 +1,52 @@
+/*
+ * include/linux/buffer-trace.h
+ *
+ * Debugging support for recording buffer_head state transitions
+ *
+ * May 2001, akpm
+ *	Created
+ */
+
+#ifndef BUFFER_TRACE_H_INCLUDED
+#define BUFFER_TRACE_H_INCLUDED
+
+#include <linux/config.h>
+
+#ifdef CONFIG_BUFFER_DEBUG
+
+/* The number of records per buffer_head. Must be a power of two */
+#define BUFFER_HISTORY_SIZE	32
+
+struct buffer_head;
+
+/* This gets embedded in struct buffer_head */
+struct buffer_history {
+	struct buffer_history_item {
+	const char *function;
+	char *info;
+	unsigned long b_state;
+	unsigned b_list:3;
+	unsigned b_jlist:4;
+	unsigned pg_dirty:1;
+	unsigned cpu:3;
+	unsigned b_count:8;
+	unsigned long b_blocknr;	/* For src != dest */
+#if defined(CONFIG_JBD2) || defined(CONFIG_JBD2_MODULE)
+	unsigned b_jcount:4;
+	unsigned b_jbd:1;
+	unsigned b_transaction:1;
+	unsigned b_next_transaction:1;
+	unsigned b_cp_transaction:1;
+	unsigned b_trans_is_running:1;
+	unsigned b_trans_is_committing:1;
+	void *b_frozen_data;
+	void *b_committed_data;
+#endif
+	} b[BUFFER_HISTORY_SIZE];
+	unsigned long b_history_head;	/* Next place to write */
+	unsigned long b_history_tail;	/* Oldest valid entry */
+};
+
+#endif	/* CONFIG_BUFFER_DEBUG */
+
+#endif	/* BUFFER_TRACE_H_INCLUDED */
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 16ed028..c814b3b 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -13,6 +13,7 @@
 #include <linux/pagemap.h>
 #include <linux/wait.h>
 #include <asm/atomic.h>
+#include <linux/buffer-trace.h>
 
 #ifdef CONFIG_BLOCK
 
@@ -69,11 +70,14 @@ struct buffer_head {
 
 	struct block_device *b_bdev;
 	bh_end_io_t *b_end_io;		/* I/O completion */
- 	void *b_private;		/* reserved for b_end_io */
+	void *b_private;		/* reserved for b_end_io */
 	struct list_head b_assoc_buffers; /* associated with another mapping */
 	struct address_space *b_assoc_map;	/* mapping this buffer is
 						   associated with */
 	atomic_t b_count;		/* users using this buffer_head */
+	#ifdef CONFIG_BUFFER_DEBUG
+	struct buffer_history b_history;
+	#endif
 };
 
 /*
diff --git a/include/linux/config.h b/include/linux/config.h
new file mode 100644
index 0000000..a91f5e5
--- /dev/null
+++ b/include/linux/config.h
@@ -0,0 +1,8 @@
+#ifndef _LINUX_CONFIG_H
+#define _LINUX_CONFIG_H
+/* This file is no longer in use and kept only for backward compatibility.
+ * autoconf.h is now included via -imacros on the commandline
+ */
+#include <linux/autoconf.h>
+
+#endif
diff --git a/include/linux/jbd.h b/include/linux/jbd.h
index 331530c..5ba749e 100644
--- a/include/linux/jbd.h
+++ b/include/linux/jbd.h
@@ -246,7 +246,7 @@ typedef struct journal_superblock_s
 
 #define J_ASSERT(assert)	BUG_ON(!(assert))
 
-#if defined(CONFIG_BUFFER_DEBUG)
+#if defined(CONFIG_BUFFER_DEBUG2)
 void buffer_assertion_failure(struct buffer_head *bh);
 #define J_ASSERT_BH(bh, expr)						\
 	do {								\
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 638ce45..58b1bbe 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -296,6 +296,7 @@ void buffer_assertion_failure(struct buffer_head *bh);
 #else
 #define J_ASSERT_BH(bh, expr)	J_ASSERT(expr)
 #define J_ASSERT_JH(jh, expr)	J_ASSERT(expr)
+#define buffer_assertion_failure(bh) do { } while (0)
 #endif
 
 #if defined(JBD2_PARANOID_IOFAIL)
@@ -1296,6 +1297,33 @@ extern int jbd_blocks_per_page(struct inode *inode);
 
 #ifdef __KERNEL__
 
+#ifdef CONFIG_BUFFER_DEBUG
+
+static inline void buffer_trace_init(struct buffer_history *bhist)
+{
+	bhist->b_history_head = 0;
+	bhist->b_history_tail = 0;
+}
+extern void buffer_trace(const char *function, struct buffer_head *dest,
+	struct buffer_head *src, char *info);
+extern void print_buffer_fields(struct buffer_head *bh);
+extern void print_buffer_trace(struct buffer_head *bh);
+
+#define BUFFER_STRINGIFY2(X)	#X
+#define BUFFER_STRINGIFY(X)	BUFFER_STRINGIFY2(X)
+
+#define BUFFER_TRACE2(dest, src, info)	\
+	do {	\
+	buffer_trace(__FUNCTION__, (dest), (src),	\
+	"["__FILE__":"	\
+	BUFFER_STRINGIFY(__LINE__)"] " info);	\
+	} while (0)
+
+#define BUFFER_TRACE(bh, info) BUFFER_TRACE2(bh, bh, info)
+#define JBUFFER_TRACE(jh, info)	BUFFER_TRACE(jh2bh(jh), info)
+
+#else	/* CONFIG_BUFFER_DEBUG */
+
 #define buffer_trace_init(bh)	do {} while (0)
 #define print_buffer_fields(bh)	do {} while (0)
 #define print_buffer_trace(bh)	do {} while (0)
@@ -1303,6 +1331,8 @@ extern int jbd_blocks_per_page(struct inode *inode);
 #define BUFFER_TRACE2(bh, bh2, info)	do {} while (0)
 #define JBUFFER_TRACE(jh, info)	do {} while (0)
 
+#endif	/* CONFIG_BUFFER_DEBUG */
+
 /* 
  * jbd2_dev_to_name is a utility function used by the jbd2 and ext4 
  * tracing infrastructure to map a dev_t to a device name.
-- 
1.9.1

Buffer-layer-tracing-support-for-JBD.patch

From e69ac38b1d3aef77fd35433a9989c1803be892db Mon Sep 17 00:00:00 2001
From: Wan Hu <wanhu@cnu.edu.cn>
Date: Wed, 30 Sep 2015 11:08:42 +0800
Subject: [PATCH] Buffer-layer-tracing-support-for-JBD

---
 fs/Kconfig                   |    4 +
 fs/Makefile                  |    1 +
 fs/jbd-kernel.c              |  253 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/buffer-trace.h |   50 ++++++++
 include/linux/buffer_head.h  |    4 +
 include/linux/jbd.h          |   30 +++++
 include/linux/jbd2.h         |    2 +-
 7 files changed, 343 insertions(+), 1 deletions(-)
 create mode 100644 fs/jbd-kernel.c
 create mode 100644 include/linux/buffer-trace.h

diff --git a/fs/Kconfig b/fs/Kconfig
index 64d44ef..6407afd 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -19,6 +19,10 @@ config FS_XIP
 source "fs/jbd/Kconfig"
 source "fs/jbd2/Kconfig"
 
+config BUFFER_DEBUG
+	bool "buffer-layer tracing"
+	depends on JBD
+
 config FS_MBCACHE
 # Meta block cache for Extended Attributes (ext2/ext3/ext4)
 	tristate
diff --git a/fs/Makefile b/fs/Makefile
index af6d047..623731d 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -36,6 +36,7 @@ obj-y				+= $(nfsd-y) $(nfsd-m)
 obj-$(CONFIG_BINFMT_AOUT)	+= binfmt_aout.o
 obj-$(CONFIG_BINFMT_EM86)	+= binfmt_em86.o
 obj-$(CONFIG_BINFMT_MISC)	+= binfmt_misc.o
+obj-$(CONFIG_BUFFER_DEBUG)	+= jbd-kernel.o
 
 # binfmt_script is always there
 obj-y				+= binfmt_script.o
diff --git a/fs/jbd-kernel.c b/fs/jbd-kernel.c
new file mode 100644
index 0000000..882f047
--- /dev/null
+++ b/fs/jbd-kernel.c
@@ -0,0 +1,253 @@
+/*
+ * fs/jbd-kernel.c
+ *
+ * Support code for the Journalling Block Device layer.
+ * This file contains things which have to be in-kernel when
+ * JBD is a module.
+ *
+ * 15 May 2001	Andrew Morton <andrewm@xxxxxxxxxx>
+ *	Created
+ */
+
+#include <linux/fs.h>
+#include <linux/jbd.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+
+/*
+ * Some sanity testing which is called from mark_buffer_clean(),
+ * and must be present in the main kernel.
+ */
+
+void jbd_preclean_buffer_check(struct buffer_head *bh)
+{
+	if (buffer_jbd(bh)) {
+		struct journal_head *jh = bh2jh(bh);
+
+		transaction_t *transaction = jh->b_transaction;
+		journal_t *journal;
+
+		if (jh->b_jlist == 0 && transaction == NULL)
+			return;
+
+		J_ASSERT_JH(jh, transaction != NULL);
+		/* The kernel may be unmapping old data. We expect it
+		 * to be dirty in that case, unless the buffer has
+		 * already been forgotten by a transaction. */
+		if (jh->b_jlist != BJ_Forget) {
+#if 1
+			if (!buffer_dirty(bh)) {
+				printk("%s: clean of clean buffer\n",
+				       __FUNCTION__);
+				print_buffer_trace(bh);
+				return;
+			}
+#endif
+			J_ASSERT_BH(bh, buffer_dirty(bh));
+		}
+
+		journal = transaction->t_journal;
+		J_ASSERT_JH(jh,
+			    transaction == journal->j_running_transaction ||
+			    transaction == journal->j_committing_transaction);
+	}
+}
+
+EXPORT_SYMBOL(jbd_preclean_buffer_check);
+
+/*
+ * Support functions for BUFFER_TRACE()
+ */
+
+static spinlock_t trace_lock = SPIN_LOCK_UNLOCKED;
+
+void buffer_trace(const char *function, struct buffer_head *dest,
+		  struct buffer_head *src, char *info)
+{
+	struct buffer_history_item *bhist_i;
+	unsigned long flags;
+
+	if (dest == 0 || src == 0)
+		return;
+
+	spin_lock_irqsave(&trace_lock, flags);
+
+	/*
+	 * Sometimes we don't initialise the ring pointers. (locally declared
+	 * temp buffer_heads). Feebly attempt to detect and correct that here.
+	 */
+	if ((dest->b_history.b_history_head - dest->b_history.b_history_tail >
+	     BUFFER_HISTORY_SIZE)) {
+		dest->b_history.b_history_head = 0;
+		dest->b_history.b_history_tail = 0;
+	}
+	bhist_i = dest->b_history.b +
+	    (dest->b_history.b_history_head & (BUFFER_HISTORY_SIZE - 1));
+	bhist_i->function = function;
+	bhist_i->info = info;
+	bhist_i->b_state = src->b_state;
+#if defined(CONFIG_JBD) || defined(CONFIG_JBD_MODULE)
+	bhist_i->b_trans_is_running = 0;
+	bhist_i->b_trans_is_committing = 0;
+	bhist_i->b_blocknr = src->b_blocknr;
+	if (buffer_jbd(src)) {
+		struct journal_head *jh;
+		journal_t *journal;
+		transaction_t *transaction;
+
+		/* Footwork to avoid racing with journal_remove_journal_head */
+		jh = src->b_private;
+		if (jh == 0)
+			goto raced;
+		transaction = jh->b_transaction;
+		if (src->b_private == 0)
+			goto raced;
+		bhist_i->b_jcount = jh->b_jcount;
+		bhist_i->b_jbd = 1;
+		bhist_i->b_jlist = jh->b_jlist;
+		bhist_i->b_frozen_data = jh->b_frozen_data;
+		bhist_i->b_committed_data = jh->b_committed_data;
+		bhist_i->b_transaction = !!jh->b_transaction;
+		bhist_i->b_next_transaction = !!jh->b_next_transaction;
+		bhist_i->b_cp_transaction = !!jh->b_cp_transaction;
+
+		if (transaction) {
+			journal = transaction->t_journal;
+			bhist_i->b_trans_is_running = transaction ==
+			    journal->j_running_transaction;
+			bhist_i->b_trans_is_committing = transaction ==
+			    journal->j_committing_transaction;
+		}
+	} else {
+raced:
+		bhist_i->b_jcount = 0;
+		bhist_i->b_jbd = 0;
+		bhist_i->b_jlist = 0;
+		bhist_i->b_frozen_data = 0;
+		bhist_i->b_committed_data = 0;
+		bhist_i->b_transaction = 0;
+		bhist_i->b_next_transaction = 0;
+		bhist_i->b_cp_transaction = 0;
+	}
+#endif /* defined(CONFIG_JBD) || defined(CONFIG_JBD_MODULE) */
+
+	bhist_i->cpu = smp_processor_id();
+	bhist_i->b_count = atomic_read(&src->b_count);
+
+	dest->b_history.b_history_head++;
+	if (dest->b_history.b_history_head - dest->b_history.b_history_tail >
+	    BUFFER_HISTORY_SIZE)
+		dest->b_history.b_history_tail =
+		    dest->b_history.b_history_head - BUFFER_HISTORY_SIZE;
+
+	spin_unlock_irqrestore(&trace_lock, flags);
+}
+
+static const char *b_jlist_to_string(unsigned int b_list)
+{
+	switch (b_list) {
+#if defined(CONFIG_JBD) || defined(CONFIG_JBD_MODULE)
+	case BJ_None:
+		return "BJ_None";
+	case BJ_SyncData:
+		return "BJ_SyncData";
+	case BJ_Metadata:
+		return "BJ_Metadata";
+	case BJ_Forget:
+		return "BJ_Forget";
+	case BJ_IO:
+		return "BJ_IO";
+	case BJ_Shadow:
+		return "BJ_Shadow";
+	case BJ_LogCtl:
+		return "BJ_LogCtl";
+	case BJ_Reserved:
+		return "BJ_Reserved";
+	case BJ_Locked:
+		return "BJ_Locked";
+#endif
+	default:
+		return "Bad b_jlist";
+	}
+}
+
+static void print_one_hist(struct buffer_history_item *bhist_i)
+{
+	printk(" %s():%s\n", bhist_i->function, bhist_i->info);
+	printk(" b_state:0x%lx b_jlist:%s cpu:%d b_count:%d b_blocknr:%lu\n",
+	       bhist_i->b_state,
+	       b_jlist_to_string(bhist_i->b_jlist),
+	       bhist_i->cpu, bhist_i->b_count, bhist_i->b_blocknr);
+#if defined(CONFIG_JBD) || defined(CONFIG_JBD_MODULE)
+	printk(" b_jbd:%u b_frozen_data:%p b_committed_data:%p\n",
+	       bhist_i->b_jbd,
+	       bhist_i->b_frozen_data, bhist_i->b_committed_data);
+	printk(" b_transaction:%u b_next_transaction:%u "
+	       "b_cp_transaction:%u b_trans_is_running:%u\n",
+	       bhist_i->b_transaction,
+	       bhist_i->b_next_transaction,
+	       bhist_i->b_cp_transaction, bhist_i->b_trans_is_running);
+	printk(" b_trans_is_comitting:%u b_jcount:%u pg_dirty:%u",
+	       bhist_i->b_trans_is_committing,
+	       bhist_i->b_jcount, bhist_i->pg_dirty);
+#endif
+	printk("\n");
+}
+
+void print_buffer_fields(struct buffer_head *bh)
+{
+	printk("b_blocknr:%llu b_count:%d\n",
+	       (unsigned long long)bh->b_blocknr, atomic_read(&bh->b_count));
+	printk("b_this_page:%p b_data:%p b_page:%p\n",
+	       bh->b_this_page, bh->b_data, bh->b_page);
+#if defined(CONFIG_JBD) || defined(CONFIG_JBD_MODULE)
+	if (buffer_jbd(bh)) {
+		struct journal_head *jh = bh2jh(bh);
+
+		printk("b_jlist:%u b_frozen_data:%p b_committed_data:%p\n",
+		       jh->b_jlist, jh->b_frozen_data, jh->b_committed_data);
+		printk(" b_transaction:%p b_next_transaction:%p "
+		       "b_cp_transaction:%p\n",
+		       jh->b_transaction, jh->b_next_transaction,
+		       jh->b_cp_transaction);
+		printk("b_cpnext:%p b_cpprev:%p\n", jh->b_cpnext, jh->b_cpprev);
+	}
+#endif
+}
+
+void print_buffer_trace(struct buffer_head *bh)
+{
+	unsigned long idx, count;
+	unsigned long flags;
+
+	printk("buffer trace for buffer at 0x%p (I am CPU %d)\n",
+	       bh, smp_processor_id());
+	BUFFER_TRACE(bh, "");	/* Record state now */
+
+	spin_lock_irqsave(&trace_lock, flags);
+	for (idx = bh->b_history.b_history_tail, count = 0;
+	     idx < bh->b_history.b_history_head &&
+	     count < BUFFER_HISTORY_SIZE; idx++, count++)
+		print_one_hist(bh->b_history.b +
+			       (idx & (BUFFER_HISTORY_SIZE - 1)));
+
+	print_buffer_fields(bh);
+	spin_unlock_irqrestore(&trace_lock, flags);
+	dump_stack();
+	printk("\n");
+}
+
+static struct buffer_head *failed_buffer_head;	/* For access with debuggers */
+
+void buffer_assertion_failure(struct buffer_head *bh)
+{
+	console_verbose();
+	failed_buffer_head = bh;
+	print_buffer_trace(bh);
+}
+
+EXPORT_SYMBOL(buffer_trace);
+EXPORT_SYMBOL(print_buffer_trace);
+EXPORT_SYMBOL(buffer_assertion_failure);
+EXPORT_SYMBOL(print_buffer_fields);
diff --git a/include/linux/buffer-trace.h b/include/linux/buffer-trace.h
new file mode 100644
index 0000000..22ca43b
--- /dev/null
+++ b/include/linux/buffer-trace.h
@@ -0,0 +1,50 @@
+/*
+ * include/linux/buffer-trace.h
+ *
+ * Debugging support for recording buffer_head state transitions
+ *
+ * May 2001, akpm
+ *	Created
+ */
+
+#ifndef BUFFER_TRACE_H_INCLUDED
+#define BUFFER_TRACE_H_INCLUDED
+
+#ifdef CONFIG_BUFFER_DEBUG
+
+/* The number of records per buffer_head. Must be a power of two */
+#define BUFFER_HISTORY_SIZE	32
+
+struct buffer_head;
+
+/* This gets embedded in struct buffer_head */
+struct buffer_history {
+	struct buffer_history_item {
+	const char *function;
+	char *info;
+	unsigned long b_state;
+	unsigned b_list:3;
+	unsigned b_jlist:4;
+	unsigned pg_dirty:1;
+	unsigned cpu:3;
+	unsigned b_count:8;
+	unsigned long b_blocknr;	/* For src != dest */
+#if defined(CONFIG_JBD) || defined(CONFIG_JBD_MODULE)
+	unsigned b_jcount:4;
+	unsigned b_jbd:1;
+	unsigned b_transaction:1;
+	unsigned b_next_transaction:1;
+	unsigned b_cp_transaction:1;
+	unsigned b_trans_is_running:1;
+	unsigned b_trans_is_committing:1;
+	void *b_frozen_data;
+	void *b_committed_data;
+#endif
+	} b[BUFFER_HISTORY_SIZE];
+	unsigned long b_history_head;	/* Next place to write */
+	unsigned long b_history_tail;	/* Oldest valid entry */
+};
+
+#endif	/* CONFIG_BUFFER_DEBUG */
+
+#endif	/* BUFFER_TRACE_H_INCLUDED */
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 16ed028..d0b717d 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -13,6 +13,7 @@
 #include <linux/pagemap.h>
 #include <linux/wait.h>
 #include <asm/atomic.h>
+#include <linux/buffer-trace.h>
 
 #ifdef CONFIG_BLOCK
 
@@ -74,6 +75,9 @@ struct buffer_head {
 	struct address_space *b_assoc_map;	/* mapping this buffer is
 						   associated with */
 	atomic_t b_count;		/* users using this buffer_head */
+#ifdef CONFIG_BUFFER_DEBUG
+	struct buffer_history b_history;
+#endif
 };
 
 /*
diff --git a/include/linux/jbd.h b/include/linux/jbd.h
index 331530c..b666b8b 100644
--- a/include/linux/jbd.h
+++ b/include/linux/jbd.h
@@ -258,6 +258,7 @@ void buffer_assertion_failure(struct buffer_head *bh);
 #else
 #define J_ASSERT_BH(bh, expr)	J_ASSERT(expr)
 #define J_ASSERT_JH(jh, expr)	J_ASSERT(expr)
+#define buffer_assertion_failure(bh) do { } while (0)
 #endif
 
 #if defined(JBD_PARANOID_IOFAIL)
@@ -1094,6 +1095,33 @@ extern int jbd_blocks_per_page(struct inode *inode);
 
 #ifdef __KERNEL__
 
+#ifdef CONFIG_BUFFER_DEBUG
+
+static inline void buffer_trace_init(struct buffer_history *bhist)
+{
+	bhist->b_history_head = 0;
+	bhist->b_history_tail = 0;
+}
+extern void buffer_trace(const char *function, struct buffer_head *dest,
+	struct buffer_head *src, char *info);
+extern void print_buffer_fields(struct buffer_head *bh);
+extern void print_buffer_trace(struct buffer_head *bh);
+
+#define BUFFER_STRINGIFY2(X)	#X
+#define BUFFER_STRINGIFY(X)	BUFFER_STRINGIFY2(X)
+
+#define BUFFER_TRACE2(dest, src, info)	\
+	do {	\
+	buffer_trace(__FUNCTION__, (dest), (src),	\
+	"["__FILE__":"	\
+	BUFFER_STRINGIFY(__LINE__)"] " info);	\
+	} while (0)
+
+#define BUFFER_TRACE(bh, info) BUFFER_TRACE2(bh, bh, info)
+#define JBUFFER_TRACE(jh, info)	BUFFER_TRACE(jh2bh(jh), info)
+
+#else	/* CONFIG_BUFFER_DEBUG */
+
 #define buffer_trace_init(bh)	do {} while (0)
 #define print_buffer_fields(bh)	do {} while (0)
 #define print_buffer_trace(bh)	do {} while (0)
@@ -1101,6 +1129,8 @@ extern int jbd_blocks_per_page(struct inode *inode);
 #define BUFFER_TRACE2(bh, bh2, info)	do {} while (0)
 #define JBUFFER_TRACE(jh, info)	do {} while (0)
 
+#endif	/* CONFIG_BUFFER_DEBUG */
+
 #endif	/* __KERNEL__ */
 
 #endif	/* _LINUX_JBD_H */
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index f1011f7..4842b1c 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -284,7 +284,7 @@ typedef struct journal_superblock_s
 
 #define J_ASSERT(assert)	BUG_ON(!(assert))
 
-#if defined(CONFIG_BUFFER_DEBUG)
+#if defined(CONFIG_BUFFER_DEBUG2)
 void buffer_assertion_failure(struct buffer_head *bh);
 #define J_ASSERT_BH(bh, expr)						\
 	do {								\
-- 
1.7.1