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Date: Wed, 11 May 2011 03:05:54 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: "surbhi.palande@...onical.com" <surbhi.palande@...onical.com>
Cc: Eric Sandeen <sandeen@...hat.com>, "jack@...e.cz" <jack@...e.cz>,
"marco.stornelli@...il.com" <marco.stornelli@...il.com>,
"adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
"toshi.okajima@...fujitsu.com" <toshi.okajima@...fujitsu.com>,
"tytso@....edu" <tytso@....edu>,
"m.mizuma@...fujitsu.com" <m.mizuma@...fujitsu.com>,
"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v3] Adding support to freeze and unfreeze a journal
On 2011-05-11, at 1:06 AM, Surbhi Palande <surbhi.palande@...onical.com> wrote:
> On 05/09/2011 06:23 PM, Eric Sandeen wrote:
>> On 5/9/11 9:51 AM, Surbhi Palande wrote:
>>> The journal should be frozen when a F.S freezes. What this means is that till
>>> the F.S is thawed again, no new transactions should be accepted by the
>>> journal. When the F.S thaws, inturn it should thaw the journal and this should
>>> allow the journal to resume accepting new transactions.
>>> While the F.S has frozen the journal, the clients of journal on calling
>>> jbd2_journal_start() will sleep on a wait queue. Thawing the journal will wake
>>> up the sleeping clients and journalling can progress normally.
>>
>> Can I ask how this was tested?
>
> Yes! I did the following on an ext4 fs mount:
> 1. fsfreeze -f $MNT
> 2. dd if=/dev/zero of=$MNT/file count=10 bs=1024 &
> 3. sync
> 4. fsfreeze -u $MNT
>
> If the dd blocks on the start_handle, then the page cache is clean and sync should have nothing to write and everything will work fine. But otherwise this should sequence should create a deadlock.
Sorry to ask the obvious question, but presumably this test fails without your patch? It isn't clear from your comment that this is the case.
> I have attempted to create a patch for xfs-test. Shall send it out as a reply to this email soon!
>
> Warm Regards,
> Surbhi.
>
>
>
>>
>> Ideally anything you found useful for testing should probably be integrated
>> into the xfstests test suite so that we don't regresss in the future.
>>
>> thanks,
>> -Eric
>>
>>> Signed-off-by: Surbhi Palande<surbhi.palande@...onical.com>
>>> ---
>>> Changes since the last patch:
>>> * Changed to the shorter forms of expressions eg: x |= y
>>> * removed the unnecessary barrier
>>>
>>> fs/ext4/super.c | 20 ++++++--------------
>>> fs/jbd2/journal.c | 1 +
>>> fs/jbd2/transaction.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>>> include/linux/jbd2.h | 10 ++++++++++
>>> 4 files changed, 59 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>>> index 8553dfb..796aa4c 100644
>>> --- a/fs/ext4/super.c
>>> +++ b/fs/ext4/super.c
>>> @@ -4179,23 +4179,15 @@ static int ext4_freeze(struct super_block *sb)
>>>
>>> journal = EXT4_SB(sb)->s_journal;
>>>
>>> - /* Now we set up the journal barrier. */
>>> - jbd2_journal_lock_updates(journal);
>>> -
>>> + error = jbd2_journal_freeze(journal);
>>> /*
>>> - * Don't clear the needs_recovery flag if we failed to flush
>>> + * Don't clear the needs_recovery flag if we failed to freeze
>>> * the journal.
>>> */
>>> - error = jbd2_journal_flush(journal);
>>> - if (error< 0)
>>> - goto out;
>>> -
>>> - /* Journal blocked and flushed, clear needs_recovery flag. */
>>> - EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
>>> - error = ext4_commit_super(sb, 1);
>>> -out:
>>> - /* we rely on s_frozen to stop further updates */
>>> - jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
>>> + if (error>= 0) {
>>> + EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
>>> + error = ext4_commit_super(sb, 1);
>>> + }
>>> return error;
>>> }
>>>
>>> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
>>> index e0ec3db..5e46333 100644
>>> --- a/fs/jbd2/journal.c
>>> +++ b/fs/jbd2/journal.c
>>> @@ -842,6 +842,7 @@ static journal_t * journal_init_common (void)
>>> init_waitqueue_head(&journal->j_wait_checkpoint);
>>> init_waitqueue_head(&journal->j_wait_commit);
>>> init_waitqueue_head(&journal->j_wait_updates);
>>> + init_waitqueue_head(&journal->j_wait_frozen);
>>> mutex_init(&journal->j_barrier);
>>> mutex_init(&journal->j_checkpoint_mutex);
>>> spin_lock_init(&journal->j_revoke_lock);
>>> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
>>> index 05fa77a..b040293 100644
>>> --- a/fs/jbd2/transaction.c
>>> +++ b/fs/jbd2/transaction.c
>>> @@ -171,6 +171,17 @@ repeat:
>>> journal->j_barrier_count == 0);
>>> goto repeat;
>>> }
>>> + /* dont let a new handle start when a journal is frozen.
>>> + * jbd2_journal_freeze calls jbd2_journal_unlock_updates() only after
>>> + * the jflags indicate that the journal is frozen. So if the
>>> + * j_barrier_count is 0, then check if this was made 0 by the freezing
>>> + * process
>>> + */
>>> + if (journal->j_flags& JBD2_FROZEN) {
>>> + read_unlock(&journal->j_state_lock);
>>> + jbd2_check_frozen(journal);
>>> + goto repeat;
>>> + }
>>>
>>> if (!journal->j_running_transaction) {
>>> read_unlock(&journal->j_state_lock);
>>> @@ -489,6 +500,37 @@ int jbd2_journal_restart(handle_t *handle, int nblocks)
>>> }
>>> EXPORT_SYMBOL(jbd2_journal_restart);
>>>
>>> +int jbd2_journal_freeze(journal_t *journal)
>>> +{
>>> + int error = 0;
>>> + /* Now we set up the journal barrier. */
>>> + jbd2_journal_lock_updates(journal);
>>> +
>>> + /*
>>> + * Don't clear the needs_recovery flag if we failed to flush
>>> + * the journal.
>>> + */
>>> + error = jbd2_journal_flush(journal);
>>> + if (error>= 0) {
>>> + write_lock(&journal->j_state_lock);
>>> + journal->j_flags |= JBD2_FROZEN;
>>> + write_unlock(&journal->j_state_lock);
>>> + }
>>> + jbd2_journal_unlock_updates(journal);
>>> + return error;
>>> +}
>>> +EXPORT_SYMBOL(jbd2_journal_freeze);
>>> +
>>> +void jbd2_journal_thaw(journal_t * journal)
>>> +{
>>> + write_lock(&journal->j_state_lock);
>>> + journal->j_flags&= ~JBD2_FROZEN;
>>> + write_unlock(&journal->j_state_lock);
>>> + wake_up(&journal->j_wait_frozen);
>>> +}
>>> +EXPORT_SYMBOL(jbd2_journal_thaw);
>>> +
>>> +
>>> /**
>>> * void jbd2_journal_lock_updates () - establish a transaction barrier.
>>> * @journal: Journal to establish a barrier on.
>>> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
>>> index a32dcae..c7885b2 100644
>>> --- a/include/linux/jbd2.h
>>> +++ b/include/linux/jbd2.h
>>> @@ -718,6 +718,7 @@ jbd2_time_diff(unsigned long start, unsigned long end)
>>> * @j_wait_checkpoint: Wait queue to trigger checkpointing
>>> * @j_wait_commit: Wait queue to trigger commit
>>> * @j_wait_updates: Wait queue to wait for updates to complete
>>> + * @j_wait_frozen: Wait queue to wait for journal to thaw
>>> * @j_checkpoint_mutex: Mutex for locking against concurrent checkpoints
>>> * @j_head: Journal head - identifies the first unused block in the journal
>>> * @j_tail: Journal tail - identifies the oldest still-used block in the
>>> @@ -835,6 +836,9 @@ struct journal_s
>>> /* Wait queue to wait for updates to complete */
>>> wait_queue_head_t j_wait_updates;
>>>
>>> + /* Wait queue to wait for journal to thaw*/
>>> + wait_queue_head_t j_wait_frozen;
>>> +
>>> /* Semaphore for locking against concurrent checkpoints */
>>> struct mutex j_checkpoint_mutex;
>>>
>>> @@ -1013,7 +1017,11 @@ struct journal_s
>>> #define JBD2_ABORT_ON_SYNCDATA_ERR 0x040 /* Abort the journal on file
>>> * data write error in ordered
>>> * mode */
>>> +#define JBD2_FROZEN 0x080 /* Journal thread is frozen as the filesystem is frozen */
>>> +
>>>
>>> +#define jbd2_check_frozen(journal) \
>>> + wait_event(journal->j_wait_frozen, (journal->j_flags& JBD2_FROZEN))
>>> /*
>>> * Function declarations for the journaling transaction and buffer
>>> * management
>>> @@ -1121,6 +1129,8 @@ extern void jbd2_journal_invalidatepage(journal_t *,
>>> struct page *, unsigned long);
>>> extern int jbd2_journal_try_to_free_buffers(journal_t *, struct page *, gfp_t);
>>> extern int jbd2_journal_stop(handle_t *);
>>> +extern int jbd2_journal_freeze(journal_t *);
>>> +extern void jbd2_journal_thaw(journal_t *);
>>> extern int jbd2_journal_flush (journal_t *);
>>> extern void jbd2_journal_lock_updates (journal_t *);
>>> extern void jbd2_journal_unlock_updates (journal_t *);
>>
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