When we reach cleanup_journal_tail(), there is no guarantee that checkpointed buffers are on a stable storage - especially if buffers were written out by log_do_checkpoint(), they are likely to be only in disk's caches. Thus when we update journal superblock, effectively removing old transaction from journal, this write of superblock can get to stable storage before those checkpointed buffers which can result in filesystem corruption after a crash. Thus we must unconditionally issue a cache flush before we update journal superblock. I managed to reproduce the corruption using somewhat tweaked Chris Mason's barrier-test scheduler. Also this should fix occasional reports of 'Bit already freed' filesystem errors which are totally unreproducible but inspection of several fs images I've gathered over time points to a problem like this. Signed-off-by: Jan Kara <jack@xxxxxxx> --- fs/jbd/checkpoint.c | 10 ++++++++++ 1 files changed, 10 insertions(+), 0 deletions(-) I've added this patch to my tree and plan to push it to Linus soon. diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c index f94fc48..3396c0f 100644 --- a/fs/jbd/checkpoint.c +++ b/fs/jbd/checkpoint.c @@ -522,6 +522,16 @@ int cleanup_journal_tail(journal_t *journal) journal->j_tail_sequence = first_tid; journal->j_tail = blocknr; spin_unlock(&journal->j_state_lock); + /* + * We need to make sure that any blocks that were recently written out + * --- perhaps by log_do_checkpoint() --- are flushed out before we + * drop the transactions from the journal. It's unlikely this will be + * necessary, especially with an appropriately sized journal, but we + * need this to guarantee correctness. Fortunately + * cleanup_journal_tail() doesn't get called all that often. + */ + if (journal->j_flags & JFS_BARRIER) + blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL); if (!(journal->j_flags & JFS_ABORT)) journal_update_superblock(journal, 1); return 0; -- 1.7.1 -- 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
