diff mbox

JBD2/JBD: race condition while writing updates to journal

Message ID 4A3E5E2B.4020106@gmail.com
State Superseded, archived
Headers show

Commit Message

dingdinghua June 21, 2009, 4:22 p.m. UTC 
At committing phase, we call jbd2_journal_write_metadata_buffer to
prepare log block's buffer_head, in this function, new_bh->b_data is set
to b_frozen_data or bh_in->b_data. We call "jbd_unlock_bh_state(bh_in)"
too early, since at this point , we haven't file bh_in to BJ_shadow list,
and we may set new_bh->b_data to bh_in->b_data, at this time, another
thread may call get write access of bh_in, modify bh_in->b_data and
dirty it. So , if new_bh->b_data is set to bh_in->b_data, the committing
transaction may flush the newly modified buffer content to disk,
preserve work done in jbd2_journal_get_write_access is useless. jbd also
has this problem.

here is the patch based on kernel version 2.6.30:

Signed-off-by: dingdinghua <dingdinghua85@gmail.com>
Acked-by: Jan Kara <jack@suse.cz>

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Comments

Theodore Ts'o June 22, 2009, 12:09 a.m. UTC | #1 
On Mon, Jun 22, 2009 at 12:22:03AM +0800, dingdinghua wrote:
> 
> At committing phase, we call jbd2_journal_write_metadata_buffer to
> prepare log block's buffer_head, in this function, new_bh->b_data is set
> to b_frozen_data or bh_in->b_data. We call "jbd_unlock_bh_state(bh_in)"
> too early, since at this point , we haven't file bh_in to BJ_shadow list,
> and we may set new_bh->b_data to bh_in->b_data, at this time, another
> thread may call get write access of bh_in, modify bh_in->b_data and
> dirty it. So , if new_bh->b_data is set to bh_in->b_data, the committing
> transaction may flush the newly modified buffer content to disk,
> preserve work done in jbd2_journal_get_write_access is useless. jbd also
> has this problem.
> 
> here is the patch based on kernel version 2.6.30:

This patch is completely whitespace damaged.  Could you resend it
using a mail user agent that doesn't damage patches, please?    Thanks!!

      	     	  	     	     	    - Ted
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diff mbox

Patch

--- fs/jbd2/journal.c.old 2009-06-21 16:18:18.000000000 +0800
+++ fs/jbd2/journal.c 2009-06-21 16:38:53.000000000 +0800
@@ -297,6 +297,8 @@  int jbd2_journal_write_metadata_buffer(t
unsigned int new_offset;
struct buffer_head *bh_in = jh2bh(jh_in);
struct jbd2_buffer_trigger_type *triggers;
+ journal_t *journal = transaction->t_journal;
+

/*
* The buffer really shouldn't be locked: only the current committing
@@ -310,6 +312,11 @@  int jbd2_journal_write_metadata_buffer(t
J_ASSERT_BH(bh_in, buffer_jbddirty(bh_in));

new_bh = alloc_buffer_head(GFP_NOFS|__GFP_NOFAIL);
+ /* keep subsequent assertions sane */
+ new_bh->b_state = 0;
+ init_buffer(new_bh, NULL, NULL);
+ atomic_set(&new_bh->b_count, 1);
+ new_jh = jbd2_journal_add_journal_head(new_bh); /* This sleeps */

/*
* If a new transaction has already done a buffer copy-out, then
@@ -388,14 +395,6 @@  repeat:
kunmap_atomic(mapped_data, KM_USER0);
}

- /* keep subsequent assertions sane */
- new_bh->b_state = 0;
- init_buffer(new_bh, NULL, NULL);
- atomic_set(&new_bh->b_count, 1);
- jbd_unlock_bh_state(bh_in);
-
- new_jh = jbd2_journal_add_journal_head(new_bh); /* This sleeps */
-
set_bh_page(new_bh, new_page, new_offset);
new_jh->b_transaction = NULL;
new_bh->b_size = jh2bh(jh_in)->b_size;
@@ -412,7 +411,11 @@  repeat:
* copying is moved to the transaction's shadow queue.
*/
JBUFFER_TRACE(jh_in, "file as BJ_Shadow");
- jbd2_journal_file_buffer(jh_in, transaction, BJ_Shadow);
+ spin_lock(&journal->j_list_lock);
+ __jbd2_journal_file_buffer(jh_in, transaction, BJ_Shadow);
+ spin_unlock(&journal->j_list_lock);
+ jbd_unlock_bh_state(bh_in);
+
JBUFFER_TRACE(new_jh, "file as BJ_IO");
jbd2_journal_file_buffer(new_jh, transaction, BJ_IO);

--- fs/jbd/journal.c.old 2009-06-21 16:27:37.000000000 +0800
+++ fs/jbd/journal.c 2009-06-21 16:45:06.000000000 +0800
@@ -287,6 +287,7 @@  int journal_write_metadata_buffer(transa
struct page *new_page;
unsigned int new_offset;
struct buffer_head *bh_in = jh2bh(jh_in);
+ journal_t *journal = transaction->t_journal;

/*
* The buffer really shouldn't be locked: only the current committing
@@ -300,6 +301,11 @@  int journal_write_metadata_buffer(transa
J_ASSERT_BH(bh_in, buffer_jbddirty(bh_in));

new_bh = alloc_buffer_head(GFP_NOFS|__GFP_NOFAIL);
+ /* keep subsequent assertions sane */
+ new_bh->b_state = 0;
+ init_buffer(new_bh, NULL, NULL);
+ atomic_set(&new_bh->b_count, 1);
+ new_jh = journal_add_journal_head(new_bh); /* This sleeps */

/*
* If a new transaction has already done a buffer copy-out, then
@@ -361,14 +367,6 @@  repeat:
kunmap_atomic(mapped_data, KM_USER0);
}

- /* keep subsequent assertions sane */
- new_bh->b_state = 0;
- init_buffer(new_bh, NULL, NULL);
- atomic_set(&new_bh->b_count, 1);
- jbd_unlock_bh_state(bh_in);
-
- new_jh = journal_add_journal_head(new_bh); /* This sleeps */
-
set_bh_page(new_bh, new_page, new_offset);
new_jh->b_transaction = NULL;
new_bh->b_size = jh2bh(jh_in)->b_size;
@@ -385,7 +383,11 @@  repeat:
* copying is moved to the transaction's shadow queue.
*/
JBUFFER_TRACE(jh_in, "file as BJ_Shadow");
- journal_file_buffer(jh_in, transaction, BJ_Shadow);
+ spin_lock(&journal->j_list_lock);
+ __journal_file_buffer(jh_in, transaction, BJ_Shadow);
+ spin_unlock(&journal->j_list_lock);
+ jbd_unlock_bh_state(bh_in);
+
JBUFFER_TRACE(new_jh, "file as BJ_IO");
journal_file_buffer(new_jh, transaction, BJ_IO);