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Date: Wed, 11 May 2011 10:06:43 +0300
From: Surbhi Palande <surbhi.palande@...onical.com>
To: Eric Sandeen <sandeen@...hat.com>
CC: jack@...e.cz, marco.stornelli@...il.com, adilger.kernel@...ger.ca,
toshi.okajima@...fujitsu.com, tytso@....edu,
m.mizuma@...fujitsu.com, linux-ext4@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3] Adding support to freeze and unfreeze a journal
Hi Eric,
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.
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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