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

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Message-ID: <CAGBYx2YjzYSXXnTCej_YzdJ+2q9cMTOG24bso7FHB4ZJwa_Ttw@mail.gmail.com>
Date:	Tue, 22 Nov 2011 09:55:17 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2] jbd: clear revoked flag on buffers before a new
 transaction started

On Tue, Nov 22, 2011 at 8:23 AM, Jan Kara <jack@...e.cz> wrote:
> 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?
YES!  I had sent out the patch for jbd2.  It seems that Ted is busy these days.

Yongqiang.
>
>                                                                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
>



-- 
Best Wishes
Yongqiang Yang
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