> On Thu, Jul 09, 2009 at 05:47:07PM +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. > > Hi Dingding, > > I split your patch into two pieces; one for jbd2 (which is in the ext4 > patch queue), and one for jbd (which is attached here). The jbd2 > patch (along with recently added patches to the ext4 patch queue) is > undergoing testing as we speak. > > Both patches look good to me, but for the ext3/jbd one, it should > probably get a second opinion. Andrew, can take a quick peek? The patch looks fine. I've added it to my tree for merging. Honza > > jbd: fix race bwtween write_metadata_buffer and get_write_access > > From: dingdinghua <dingdinghua85@xxxxxxxxx> > > 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 <dingdinghua85@xxxxxxxxx> > Acked-by: "Theodore Ts'o" <tytso@xxxxxxx> > --- > > diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c > index 737f724..ff5dcb5 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 @@ 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); > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Jan Kara <jack@xxxxxxx> SuSE CR Labs -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
