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SubjectRe: [patch 16/67] jbd: fix commit of ordered data buffers
  Hi,

> -stable review patch. If anyone has any objections, please let us know.
There does not seem to be any obvious issues with this change and it
fixes a real BUG happenning during some stress-testing. On the other hand
the change is kind of intrusive and changes a quite complex code (or
better said code with complex interactions). So I'm not sure if it really is
-stable material...

Honza

> ------------------
> From: Jan Kara <jack@suse.cz>
>
> Original commit code assumes, that when a buffer on BJ_SyncData list is
> locked, it is being written to disk. But this is not true and hence it can
> lead to a potential data loss on crash. Also the code didn't count with
> the fact that journal_dirty_data() can steal buffers from committing
> transaction and hence could write buffers that no longer belong to the
> committing transaction. Finally it could possibly happen that we tried
> writing out one buffer several times.
>
> The patch below tries to solve these problems by a complete rewrite of the
> data commit code. We go through buffers on t_sync_datalist, lock buffers
> needing write out and store them in an array. Buffers are also immediately
> refiled to BJ_Locked list or unfiled (if the write out is completed). When
> the array is full or we have to block on buffer lock, we submit all
> accumulated buffers for IO.
>
> [suitable for 2.6.18.x around the 2.6.19-rc2 timeframe]
>
> Signed-off-by: Jan Kara <jack@suse.cz>
> Cc: Badari Pulavarty <pbadari@us.ibm.com>
> Signed-off-by: Andrew Morton <akpm@osdl.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
>
> ---
> fs/jbd/commit.c | 182 ++++++++++++++++++++++++++++++++++----------------------
> 1 file changed, 113 insertions(+), 69 deletions(-)
>
> --- linux-2.6.18.orig/fs/jbd/commit.c
> +++ linux-2.6.18/fs/jbd/commit.c
> @@ -160,6 +160,117 @@ static int journal_write_commit_record(j
> return (ret == -EIO);
> }
>
> +void journal_do_submit_data(struct buffer_head **wbuf, int bufs)
> +{
> + int i;
> +
> + for (i = 0; i < bufs; i++) {
> + wbuf[i]->b_end_io = end_buffer_write_sync;
> + /* We use-up our safety reference in submit_bh() */
> + submit_bh(WRITE, wbuf[i]);
> + }
> +}
> +
> +/*
> + * Submit all the data buffers to disk
> + */
> +static void journal_submit_data_buffers(journal_t *journal,
> + transaction_t *commit_transaction)
> +{
> + struct journal_head *jh;
> + struct buffer_head *bh;
> + int locked;
> + int bufs = 0;
> + struct buffer_head **wbuf = journal->j_wbuf;
> +
> + /*
> + * Whenever we unlock the journal and sleep, things can get added
> + * onto ->t_sync_datalist, so we have to keep looping back to
> + * write_out_data until we *know* that the list is empty.
> + *
> + * Cleanup any flushed data buffers from the data list. Even in
> + * abort mode, we want to flush this out as soon as possible.
> + */
> +write_out_data:
> + cond_resched();
> + spin_lock(&journal->j_list_lock);
> +
> + while (commit_transaction->t_sync_datalist) {
> + jh = commit_transaction->t_sync_datalist;
> + bh = jh2bh(jh);
> + locked = 0;
> +
> + /* Get reference just to make sure buffer does not disappear
> + * when we are forced to drop various locks */
> + get_bh(bh);
> + /* If the buffer is dirty, we need to submit IO and hence
> + * we need the buffer lock. We try to lock the buffer without
> + * blocking. If we fail, we need to drop j_list_lock and do
> + * blocking lock_buffer().
> + */
> + if (buffer_dirty(bh)) {
> + if (test_set_buffer_locked(bh)) {
> + BUFFER_TRACE(bh, "needs blocking lock");
> + spin_unlock(&journal->j_list_lock);
> + /* Write out all data to prevent deadlocks */
> + journal_do_submit_data(wbuf, bufs);
> + bufs = 0;
> + lock_buffer(bh);
> + spin_lock(&journal->j_list_lock);
> + }
> + locked = 1;
> + }
> + /* We have to get bh_state lock. Again out of order, sigh. */
> + if (!inverted_lock(journal, bh)) {
> + jbd_lock_bh_state(bh);
> + spin_lock(&journal->j_list_lock);
> + }
> + /* Someone already cleaned up the buffer? */
> + if (!buffer_jbd(bh)
> + || jh->b_transaction != commit_transaction
> + || jh->b_jlist != BJ_SyncData) {
> + jbd_unlock_bh_state(bh);
> + if (locked)
> + unlock_buffer(bh);
> + BUFFER_TRACE(bh, "already cleaned up");
> + put_bh(bh);
> + continue;
> + }
> + if (locked && test_clear_buffer_dirty(bh)) {
> + BUFFER_TRACE(bh, "needs writeout, adding to array");
> + wbuf[bufs++] = bh;
> + __journal_file_buffer(jh, commit_transaction,
> + BJ_Locked);
> + jbd_unlock_bh_state(bh);
> + if (bufs == journal->j_wbufsize) {
> + spin_unlock(&journal->j_list_lock);
> + journal_do_submit_data(wbuf, bufs);
> + bufs = 0;
> + goto write_out_data;
> + }
> + }
> + else {
> + BUFFER_TRACE(bh, "writeout complete: unfile");
> + __journal_unfile_buffer(jh);
> + jbd_unlock_bh_state(bh);
> + if (locked)
> + unlock_buffer(bh);
> + journal_remove_journal_head(bh);
> + /* Once for our safety reference, once for
> + * journal_remove_journal_head() */
> + put_bh(bh);
> + put_bh(bh);
> + }
> +
> + if (lock_need_resched(&journal->j_list_lock)) {
> + spin_unlock(&journal->j_list_lock);
> + goto write_out_data;
> + }
> + }
> + spin_unlock(&journal->j_list_lock);
> + journal_do_submit_data(wbuf, bufs);
> +}
> +
> /*
> * journal_commit_transaction
> *
> @@ -313,80 +424,13 @@ void journal_commit_transaction(journal_
> * Now start flushing things to disk, in the order they appear
> * on the transaction lists. Data blocks go first.
> */
> -
> err = 0;
> - /*
> - * Whenever we unlock the journal and sleep, things can get added
> - * onto ->t_sync_datalist, so we have to keep looping back to
> - * write_out_data until we *know* that the list is empty.
> - */
> - bufs = 0;
> - /*
> - * Cleanup any flushed data buffers from the data list. Even in
> - * abort mode, we want to flush this out as soon as possible.
> - */
> -write_out_data:
> - cond_resched();
> - spin_lock(&journal->j_list_lock);
> -
> - while (commit_transaction->t_sync_datalist) {
> - struct buffer_head *bh;
> -
> - jh = commit_transaction->t_sync_datalist;
> - commit_transaction->t_sync_datalist = jh->b_tnext;
> - bh = jh2bh(jh);
> - if (buffer_locked(bh)) {
> - BUFFER_TRACE(bh, "locked");
> - if (!inverted_lock(journal, bh))
> - goto write_out_data;
> - __journal_temp_unlink_buffer(jh);
> - __journal_file_buffer(jh, commit_transaction,
> - BJ_Locked);
> - jbd_unlock_bh_state(bh);
> - if (lock_need_resched(&journal->j_list_lock)) {
> - spin_unlock(&journal->j_list_lock);
> - goto write_out_data;
> - }
> - } else {
> - if (buffer_dirty(bh)) {
> - BUFFER_TRACE(bh, "start journal writeout");
> - get_bh(bh);
> - wbuf[bufs++] = bh;
> - if (bufs == journal->j_wbufsize) {
> - jbd_debug(2, "submit %d writes\n",
> - bufs);
> - spin_unlock(&journal->j_list_lock);
> - ll_rw_block(SWRITE, bufs, wbuf);
> - journal_brelse_array(wbuf, bufs);
> - bufs = 0;
> - goto write_out_data;
> - }
> - } else {
> - BUFFER_TRACE(bh, "writeout complete: unfile");
> - if (!inverted_lock(journal, bh))
> - goto write_out_data;
> - __journal_unfile_buffer(jh);
> - jbd_unlock_bh_state(bh);
> - journal_remove_journal_head(bh);
> - put_bh(bh);
> - if (lock_need_resched(&journal->j_list_lock)) {
> - spin_unlock(&journal->j_list_lock);
> - goto write_out_data;
> - }
> - }
> - }
> - }
> -
> - if (bufs) {
> - spin_unlock(&journal->j_list_lock);
> - ll_rw_block(SWRITE, bufs, wbuf);
> - journal_brelse_array(wbuf, bufs);
> - spin_lock(&journal->j_list_lock);
> - }
> + journal_submit_data_buffers(journal, commit_transaction);
>
> /*
> * Wait for all previously submitted IO to complete.
> */
> + spin_lock(&journal->j_list_lock);
> while (commit_transaction->t_locked_list) {
> struct buffer_head *bh;
>
>
> --
--
Jan Kara <jack@suse.cz>
SuSE CR Labs
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