On Tue 15-11-11 16:02:31, Yongqiang Yang wrote:
> A revoked block in a transaction means the block is deleted by filesystem
> in the transaction. If the block is reused in the same transaction, we
> need to cancel revoke status of the block. We also should prohibit a block
> from being revoked more than once in a transaction. So we need to look up
> the revoke table to check if a given block is revoked, to acceletate the
> looking up, jbd/jbd2 use revoked flag to cache status of a block.
>
I'd alter the change log here:
Currently, we clear revoked status only when a block is reused. However,
this can trigger a false journal error: Consider a situation when a block
is used as a metadata block, is deleted (revoked) in ordered mode, and 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 revoked status more uptodate - we clear
buffers' revoke bit when switching revoke tables to reflect that no buffers
are revoked in the current transaction anymore.
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
> ---
> fs/jbd/commit.c | 5 +++++
> fs/jbd/revoke.c | 28 ++++++++++++++++++++++++++++
> include/linux/jbd.h | 1 +
> 3 files changed, 34 insertions(+), 0 deletions(-)
>
> diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
> index 8799207..075b7e8 100644
> --- a/fs/jbd/commit.c
> +++ b/fs/jbd/commit.c
> @@ -392,6 +392,11 @@ void journal_commit_transaction(journal_t *journal)
> jbd_debug (3, "JBD: commit phase 1\n");
>
> /*
> + * Clear revoked flag.
This comment does not explain nothing not obvious from the code. But we
should explain here *why* we need to clear the flags:
We clear revoke status cached in b_state here to reflect that no buffer
is revoked in the next transaction which is going to be started.
> + */
> + journal_clear_revoked_flag(journal);
Maybe call the function journal_clear_buffer_revoked_flags()?
> +
> + /*
> * 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..cf73b67 100644
> --- a/fs/jbd/revoke.c
> +++ b/fs/jbd/revoke.c
> @@ -474,6 +474,34 @@ 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.
> + */
Comment style is:
/*
* some text
* more text
*/
> +void journal_clear_revoked_flag(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..de59ac0 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_revoked_flag(journal_t *journal);
>
> /*
> * The log thread user interface:
Also please extend a comment (around line 50 in fs/jbd/journal.c) by:
We cache revoke status of a buffer in the current transaction in b_state
bits. Revoke information on buffers...
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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