linux-ext4 - Re: [PATCH v2] jbd: clear revoked flag on buffers before a new transaction started

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Date:	Tue, 22 Nov 2011 01:23:26 +0100
From:	Jan Kara <jack@...e.cz>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
Cc:	jack@...e.cz, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2] jbd: clear revoked flag on buffers before a new
 transaction started

On Sat 19-11-11 17:34:29, Yongqiang Yang wrote:
> Currently, we clear revoked flag only when a block is reused.  However,
> this can tigger a false journal error.  Consider a situation when a block
> is used as a meta block and is deleted(revoked) in ordered mode, then the
> block is allocated as a data block to a file.  At this moment, user changes
> the file's journal mode from ordered to journaled and truncates the file.
> The block will be considered re-revoked by journal because it has revoked
> flag still pending from the last transaction and an assertion triggers.
> 
> We fix the problem by keeping the revoked status more uptodate - we clear
> revoked flag when switching revoke tables to reflect there is no revoked
> buffers in current transaction any more.
  Thanks. Merged into my tree. Will you create the same patch for JBD2 as
well?

								Honza

> 
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
> ---
>  fs/jbd/commit.c     |    6 ++++++
>  fs/jbd/revoke.c     |   34 ++++++++++++++++++++++++++++++++++
>  include/linux/jbd.h |    1 +
>  3 files changed, 41 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
> index 8799207..f2b9a57 100644
> --- a/fs/jbd/commit.c
> +++ b/fs/jbd/commit.c
> @@ -392,6 +392,12 @@ void journal_commit_transaction(journal_t *journal)
>  	jbd_debug (3, "JBD: commit phase 1\n");
>  
>  	/*
> +	 * Clear revoked flag to reflect there is no revoked buffers
> +	 * in the next transaction which is going to be started.
> +	 */
> +	journal_clear_buffer_revoked_flags(journal);
> +
> +	/*
>  	 * Switch to a new revoke table.
>  	 */
>  	journal_switch_revoke_table(journal);
> diff --git a/fs/jbd/revoke.c b/fs/jbd/revoke.c
> index 034eb82..501d363 100644
> --- a/fs/jbd/revoke.c
> +++ b/fs/jbd/revoke.c
> @@ -47,6 +47,10 @@
>   *   overwriting the new data.  We don't even need to clear the revoke
>   *   bit here.
>   *
> + * We cache revoke status of a buffer in the current transaction in b_states
> + * bits.  As the name says, revokevalid flag indicates that the cached revoke
> + * status of a buffer is valid and we can rely on the cached status.
> + *
>   * Revoke information on buffers is a tri-state value:
>   *
>   * RevokeValid clear:	no cached revoke status, need to look it up
> @@ -474,6 +478,36 @@ int journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
>  	return did_revoke;
>  }
>  
> +/*
> + * journal_clear_revoked_flag clears revoked flag of buffers in
> + * revoke table to reflect there is no revoked buffers in the next
> + * transaction which is going to be started.
> + */
> +void journal_clear_buffer_revoked_flags(journal_t *journal)
> +{
> +	struct jbd_revoke_table_s *revoke = journal->j_revoke;
> +	int i = 0;
> +
> +	for (i = 0; i < revoke->hash_size; i++) {
> +		struct list_head *hash_list;
> +		struct list_head *list_entry;
> +		hash_list = &revoke->hash_table[i];
> +
> +		list_for_each(list_entry, hash_list) {
> +			struct jbd_revoke_record_s *record;
> +			struct buffer_head *bh;
> +			record = (struct jbd_revoke_record_s *)list_entry;
> +			bh = __find_get_block(journal->j_fs_dev,
> +					      record->blocknr,
> +					      journal->j_blocksize);
> +			if (bh) {
> +				clear_buffer_revoked(bh);
> +				__brelse(bh);
> +			}
> +		}
> +	}
> +}
> +
>  /* journal_switch_revoke table select j_revoke for next transaction
>   * we do not want to suspend any processing until all revokes are
>   * written -bzzz
> diff --git a/include/linux/jbd.h b/include/linux/jbd.h
> index 0f9f0b6..5aa964e 100644
> --- a/include/linux/jbd.h
> +++ b/include/linux/jbd.h
> @@ -918,6 +918,7 @@ extern int	journal_set_revoke(journal_t *, unsigned int, tid_t);
>  extern int	journal_test_revoke(journal_t *, unsigned int, tid_t);
>  extern void	journal_clear_revoke(journal_t *);
>  extern void	journal_switch_revoke_table(journal_t *journal);
> +extern void	journal_clear_buffer_revoked_flags(journal_t *journal);
>  
>  /*
>   * The log thread user interface:
> -- 
> 1.7.5.1
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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