From f1015c447781729060c415f5133164c638561f25 Mon Sep 17 00:00:00 2001 From: dingdinghua Date: Wed, 15 Jul 2009 21:42:05 +0200 Subject: [PATCH] jbd: fix race between write_metadata_buffer and get_write_access The function journal_write_metadata_buffer() calls jbd_unlock_bh_state(bh_in) too early; this could potentially allow another thread to call get_write_access on the buffer head, modify the data, and dirty it, and allowing the wrong data to be written into the journal. Fortunately, if we lose this race, the only time this will actually cause filesystem corruption is if there is a system crash or other unclean shutdown of the system before the next commit can take place. Signed-off-by: dingdinghua Acked-by: "Theodore Ts'o" Signed-off-by: Jan Kara --- fs/jbd/journal.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c index 94a64a199a63..f96f85092d1c 100644 --- a/fs/jbd/journal.c +++ b/fs/jbd/journal.c @@ -287,6 +287,7 @@ int journal_write_metadata_buffer(transaction_t *transaction, 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(transaction_t *transaction, 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 @@ int journal_write_metadata_buffer(transaction_t *transaction, 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 @@ int journal_write_metadata_buffer(transaction_t *transaction, * 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); -- GitLab