jbd2/ocfs2: Fix block checksumming when a buffer is used in several transactions

OCFS2 uses t_commit trigger to compute and store checksum of the just
committed blocks. When a buffer has b_frozen_data, checksum is computed
for it instead of b_data but this can result in an old checksum being
written to the filesystem in the following scenario:

1) transaction1 is opened
2) handle1 is opened
3) journal_access(handle1, bh)
    - This sets jh->b_transaction to transaction1
4) modify(bh)
5) journal_dirty(handle1, bh)
6) handle1 is closed
7) start committing transaction1, opening transaction2
8) handle2 is opened
9) journal_access(handle2, bh)
    - This copies off b_frozen_data to make it safe for transaction1 to commit.
      jh->b_next_transaction is set to transaction2.
10) jbd2_journal_write_metadata() checksums b_frozen_data
11) the journal correctly writes b_frozen_data to the disk journal
12) handle2 is closed
    - There was no dirty call for the bh on handle2, so it is never queued for
      any more journal operation
13) Checkpointing finally happens, and it just spools the bh via normal buffer
writeback.  This will write b_data, which was never triggered on and thus
contains a wrong (old) checksum.

This patch fixes the problem by calling the trigger at the moment data is
frozen for journal commit - i.e., either when b_frozen_data is created by
do_get_write_access or just before we write a buffer to the log if
b_frozen_data does not exist. We also rename the trigger to t_frozen as
that better describes when it is called.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

fs/jbd2/journal.c

@@ -297,7 +297,6 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
 	struct page *new_page;
 	unsigned int new_offset;
 	struct buffer_head *bh_in = jh2bh(jh_in);
-	struct jbd2_buffer_trigger_type *triggers;
 	journal_t *journal = transaction->t_journal;
 
 	/*
@@ -328,21 +327,21 @@ repeat:
 		done_copy_out = 1;
 		new_page = virt_to_page(jh_in->b_frozen_data);
 		new_offset = offset_in_page(jh_in->b_frozen_data);
-		triggers = jh_in->b_frozen_triggers;
 	} else {
 		new_page = jh2bh(jh_in)->b_page;
 		new_offset = offset_in_page(jh2bh(jh_in)->b_data);
-		triggers = jh_in->b_triggers;
 	}
 
 	mapped_data = kmap_atomic(new_page, KM_USER0);
 	/*
-	 * Fire any commit trigger.  Do this before checking for escaping,
-	 * as the trigger may modify the magic offset.  If a copy-out
-	 * happens afterwards, it will have the correct data in the buffer.
+	 * Fire data frozen trigger if data already wasn't frozen.  Do this
+	 * before checking for escaping, as the trigger may modify the magic
+	 * offset.  If a copy-out happens afterwards, it will have the correct
+	 * data in the buffer.
 	 */
-	jbd2_buffer_commit_trigger(jh_in, mapped_data + new_offset,
-				   triggers);
+	if (!done_copy_out)
+		jbd2_buffer_frozen_trigger(jh_in, mapped_data + new_offset,
+					   jh_in->b_triggers);
 
 	/*
 	 * Check for escaping

fs/jbd2/transaction.c

@@ -725,6 +725,9 @@ done:
 		page = jh2bh(jh)->b_page;
 		offset = ((unsigned long) jh2bh(jh)->b_data) & ~PAGE_MASK;
 		source = kmap_atomic(page, KM_USER0);
+		/* Fire data frozen trigger just before we copy the data */
+		jbd2_buffer_frozen_trigger(jh, source + offset,
+					   jh->b_triggers);
 		memcpy(jh->b_frozen_data, source+offset, jh2bh(jh)->b_size);
 		kunmap_atomic(source, KM_USER0);
 
@@ -963,15 +966,15 @@ void jbd2_journal_set_triggers(struct buffer_head *bh,
 	jh->b_triggers = type;
 }
 
-void jbd2_buffer_commit_trigger(struct journal_head *jh, void *mapped_data,
+void jbd2_buffer_frozen_trigger(struct journal_head *jh, void *mapped_data,
 				struct jbd2_buffer_trigger_type *triggers)
 {
 	struct buffer_head *bh = jh2bh(jh);
 
-	if (!triggers || !triggers->t_commit)
+	if (!triggers || !triggers->t_frozen)
 		return;
 
-	triggers->t_commit(triggers, bh, mapped_data, bh->b_size);
+	triggers->t_frozen(triggers, bh, mapped_data, bh->b_size);
 }
 
 void jbd2_buffer_abort_trigger(struct journal_head *jh,

fs/ocfs2/journal.c

@@ -472,7 +472,7 @@ static inline struct ocfs2_triggers *to_ocfs2_trigger(struct jbd2_buffer_trigger
 	return container_of(triggers, struct ocfs2_triggers, ot_triggers);
 }
 
-static void ocfs2_commit_trigger(struct jbd2_buffer_trigger_type *triggers,
+static void ocfs2_frozen_trigger(struct jbd2_buffer_trigger_type *triggers,
 				 struct buffer_head *bh,
 				 void *data, size_t size)
 {
@@ -491,7 +491,7 @@ static void ocfs2_commit_trigger(struct jbd2_buffer_trigger_type *triggers,
  * Quota blocks have their own trigger because the struct ocfs2_block_check
  * offset depends on the blocksize.
  */
-static void ocfs2_dq_commit_trigger(struct jbd2_buffer_trigger_type *triggers,
+static void ocfs2_dq_frozen_trigger(struct jbd2_buffer_trigger_type *triggers,
 				 struct buffer_head *bh,
 				 void *data, size_t size)
 {
@@ -511,7 +511,7 @@ static void ocfs2_dq_commit_trigger(struct jbd2_buffer_trigger_type *triggers,
  * Directory blocks also have their own trigger because the
  * struct ocfs2_block_check offset depends on the blocksize.
  */
-static void ocfs2_db_commit_trigger(struct jbd2_buffer_trigger_type *triggers,
+static void ocfs2_db_frozen_trigger(struct jbd2_buffer_trigger_type *triggers,
 				 struct buffer_head *bh,
 				 void *data, size_t size)
 {
@@ -544,7 +544,7 @@ static void ocfs2_abort_trigger(struct jbd2_buffer_trigger_type *triggers,
 
 static struct ocfs2_triggers di_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_commit_trigger,
+		.t_frozen = ocfs2_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 	.ot_offset	= offsetof(struct ocfs2_dinode, i_check),
@@ -552,7 +552,7 @@ static struct ocfs2_triggers di_triggers = {
 
 static struct ocfs2_triggers eb_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_commit_trigger,
+		.t_frozen = ocfs2_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 	.ot_offset	= offsetof(struct ocfs2_extent_block, h_check),
@@ -560,7 +560,7 @@ static struct ocfs2_triggers eb_triggers = {
 
 static struct ocfs2_triggers rb_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_commit_trigger,
+		.t_frozen = ocfs2_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 	.ot_offset	= offsetof(struct ocfs2_refcount_block, rf_check),
@@ -568,7 +568,7 @@ static struct ocfs2_triggers rb_triggers = {
 
 static struct ocfs2_triggers gd_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_commit_trigger,
+		.t_frozen = ocfs2_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 	.ot_offset	= offsetof(struct ocfs2_group_desc, bg_check),
@@ -576,14 +576,14 @@ static struct ocfs2_triggers gd_triggers = {
 
 static struct ocfs2_triggers db_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_db_commit_trigger,
+		.t_frozen = ocfs2_db_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 };
 
 static struct ocfs2_triggers xb_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_commit_trigger,
+		.t_frozen = ocfs2_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 	.ot_offset	= offsetof(struct ocfs2_xattr_block, xb_check),
@@ -591,14 +591,14 @@ static struct ocfs2_triggers xb_triggers = {
 
 static struct ocfs2_triggers dq_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_dq_commit_trigger,
+		.t_frozen = ocfs2_dq_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 };
 
 static struct ocfs2_triggers dr_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_commit_trigger,
+		.t_frozen = ocfs2_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 	.ot_offset	= offsetof(struct ocfs2_dx_root_block, dr_check),
@@ -606,7 +606,7 @@ static struct ocfs2_triggers dr_triggers = {
 
 static struct ocfs2_triggers dl_triggers = {
 	.ot_triggers = {
-		.t_commit = ocfs2_commit_trigger,
+		.t_frozen = ocfs2_frozen_trigger,
 		.t_abort = ocfs2_abort_trigger,
 	},
 	.ot_offset	= offsetof(struct ocfs2_dx_leaf, dl_check),

include/linux/jbd2.h

@@ -1026,11 +1026,12 @@ void __jbd2_journal_insert_checkpoint(struct journal_head *, transaction_t *);
 
 struct jbd2_buffer_trigger_type {
 	/*
-	 * Fired just before a buffer is written to the journal.
-	 * mapped_data is a mapped buffer that is the frozen data for
-	 * commit.
+	 * Fired a the moment data to write to the journal are known to be
+	 * stable - so either at the moment b_frozen_data is created or just
+	 * before a buffer is written to the journal.  mapped_data is a mapped
+	 * buffer that is the frozen data for commit.
 	 */
-	void (*t_commit)(struct jbd2_buffer_trigger_type *type,
+	void (*t_frozen)(struct jbd2_buffer_trigger_type *type,
 			 struct buffer_head *bh, void *mapped_data,
 			 size_t size);
 
@@ -1042,7 +1043,7 @@ struct jbd2_buffer_trigger_type {
 			struct buffer_head *bh);
 };
 
-extern void jbd2_buffer_commit_trigger(struct journal_head *jh,
+extern void jbd2_buffer_frozen_trigger(struct journal_head *jh,
 				       void *mapped_data,
 				       struct jbd2_buffer_trigger_type *triggers);
 extern void jbd2_buffer_abort_trigger(struct journal_head *jh,