Patchwork [v2] Adding support to freeze and unfreeze a journal

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Submitter Surbhi Palande
Date May 7, 2011, 8:04 p.m.
Message ID <1304798662-3884-1-git-send-email-surbhi.palande@canonical.com>
Download mbox | patch
Permalink /patch/94505/
State Superseded
Headers show

Comments

Surbhi Palande - May 7, 2011, 8:04 p.m.
On freezing the F.S, the journal should be frozen as well. This implies not
being able to start any new transactions on a frozen journal. Similarly,
thawing a F.S should thaw a journal and this should conversely start accepting
new transactions. While the F.S is frozen any request to start a new
handle should end up on a wait queue till the F.S is thawed back again.

Adding support to freeze and thaw a journal and leveraging this support in
freezing and thawing ext4.

Signed-off-by: Surbhi Palande <surbhi.palande@canonical.com>
---
Changes since v1:
* Check for the j_flag and if frozen release the j_state_lock before sleeping
   on wait queue
* Export the freeze, thaw routines
* Added a barrier after setting the j_flags = JBD2_FROZEN

 fs/ext4/super.c       |   20 ++++++--------------
 fs/jbd2/journal.c     |    1 +
 fs/jbd2/transaction.c |   43 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/jbd2.h  |    9 +++++++++
 4 files changed, 59 insertions(+), 14 deletions(-)
Marco Stornelli - May 8, 2011, 8:24 a.m.
Il 07/05/2011 22:04, Surbhi Palande ha scritto:
> On freezing the F.S, the journal should be frozen as well. This implies not
> being able to start any new transactions on a frozen journal. Similarly,
> thawing a F.S should thaw a journal and this should conversely start accepting
> new transactions. While the F.S is frozen any request to start a new
> handle should end up on a wait queue till the F.S is thawed back again.
>
> Adding support to freeze and thaw a journal and leveraging this support in
> freezing and thawing ext4.
>
> Signed-off-by: Surbhi Palande<surbhi.palande@canonical.com>
> ---
> Changes since v1:
> * Check for the j_flag and if frozen release the j_state_lock before sleeping
>     on wait queue
> * Export the freeze, thaw routines
> * Added a barrier after setting the j_flags = JBD2_FROZEN
>
>   fs/ext4/super.c       |   20 ++++++--------------
>   fs/jbd2/journal.c     |    1 +
>   fs/jbd2/transaction.c |   43 +++++++++++++++++++++++++++++++++++++++++++
>   include/linux/jbd2.h  |    9 +++++++++
>   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..3283c77 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 +500,38 @@ 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 = journal->j_flags | JBD2_FROZEN;

Better 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 = journal->j_flags&= ~JBD2_FROZEN;

What? Maybe journal->j_flags &= ~JBD2_FROZEN;

> +	write_unlock(&journal->j_state_lock);
> +	smp_wmb();

It'd be better to add a comment here for this barrier.

> +	wake_up(&journal->j_wait_frozen);
> +}
> +EXPORT_SYMBOL(jbd2_journal_thaw);
> +
> +

Marco
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Surbhi Palande - May 9, 2011, 9:04 a.m.
On 05/08/2011 11:24 AM, Marco Stornelli wrote:

Thanks for your review!
> Il 07/05/2011 22:04, Surbhi Palande ha scritto:
>> On freezing the F.S, the journal should be frozen as well. This
>> implies not
>> being able to start any new transactions on a frozen journal. Similarly,
>> thawing a F.S should thaw a journal and this should conversely start
>> accepting
>> new transactions. While the F.S is frozen any request to start a new
>> handle should end up on a wait queue till the F.S is thawed back again.
>>
>> Adding support to freeze and thaw a journal and leveraging this
>> support in
>> freezing and thawing ext4.
>>
>> Signed-off-by: Surbhi Palande<surbhi.palande@canonical.com>
>> ---
>> Changes since v1:
>> * Check for the j_flag and if frozen release the j_state_lock before
>> sleeping
>> on wait queue
>> * Export the freeze, thaw routines
>> * Added a barrier after setting the j_flags = JBD2_FROZEN
>>
>> fs/ext4/super.c | 20 ++++++--------------
>> fs/jbd2/journal.c | 1 +
>> fs/jbd2/transaction.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>> include/linux/jbd2.h | 9 +++++++++
>> 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..3283c77 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 +500,38 @@ 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 = journal->j_flags | JBD2_FROZEN;
>
> Better journal->j_flags |= JBD2_FROZEN;

I was wondering why this is actually better than the longer form? Is 
there any technical reason other than preference of coding style here?

>
>> + 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 = journal->j_flags&= ~JBD2_FROZEN;
>
> What? Maybe journal->j_flags &= ~JBD2_FROZEN;

This definitely is a typo and needs a change. Again, why do you 
recommend the shorter form?

>
>> + write_unlock(&journal->j_state_lock);
>> + smp_wmb();
>
> It'd be better to add a comment here for this barrier.
Ok!
>
>> + wake_up(&journal->j_wait_frozen);
>> +}
>> +EXPORT_SYMBOL(jbd2_journal_thaw);
>> +
>> +
>
> Marco
Warm Regards,
Surbhi.

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Jan Kara - May 9, 2011, 9:24 a.m.
On Mon 09-05-11 12:04:45, Surbhi Palande wrote:
> On 05/08/2011 11:24 AM, Marco Stornelli wrote:
> >>+ error = jbd2_journal_flush(journal);
> >>+ if (error>= 0) {
> >>+ write_lock(&journal->j_state_lock);
> >>+ journal->j_flags = journal->j_flags | JBD2_FROZEN;
> >
> >Better journal->j_flags |= JBD2_FROZEN;
> 
> I was wondering why this is actually better than the longer form? Is
> there any technical reason other than preference of coding style
> here?
  It's just a coding style but that's kind of important as well. You don't
have to employ your brain by checking whether the right hand side is the
same as the left hand side in this case. So please use |=.

								Honza
Jan Kara - May 9, 2011, 9:53 a.m.
On Sat 07-05-11 23:04:22, Surbhi Palande wrote:
> +void jbd2_journal_thaw(journal_t * journal)
> +{
> +	write_lock(&journal->j_state_lock);
> +	journal->j_flags = journal->j_flags &= ~JBD2_FROZEN;
> +	write_unlock(&journal->j_state_lock);
> +	smp_wmb();
  Why is here the smp_wmb()? The write is inside a rw-lock so it cannot be
reordered. Also wake_up() is protected by queue->lock so I don't see the
need for a barrier.

> +	wake_up(&journal->j_wait_frozen);
> +}
> +EXPORT_SYMBOL(jbd2_journal_thaw);

								Honza
Surbhi Palande - May 9, 2011, 1:49 p.m.
On 05/09/2011 12:53 PM, Jan Kara wrote:
> On Sat 07-05-11 23:04:22, Surbhi Palande wrote:
>> +void jbd2_journal_thaw(journal_t * journal)
>> +{
>> +	write_lock(&journal->j_state_lock);
>> +	journal->j_flags = journal->j_flags&= ~JBD2_FROZEN;
>> +	write_unlock(&journal->j_state_lock);
>> +	smp_wmb();
>    Why is here the smp_wmb()? The write is inside a rw-lock so it cannot be
> reordered. Also wake_up() is protected by queue->lock so I don't see the
> need for a barrier.

Ok, thanks for letting me know. I was under the impression that a 
reorder was possible in case of SMP. I will rewrite the patch with this 
change and the one that Marco Stornelli suggested as well.

Thanks a lot!

Warm Regards,
Surbhi.

>
>> +	wake_up(&journal->j_wait_frozen);
>> +}
>> +EXPORT_SYMBOL(jbd2_journal_thaw);
>
> 								Honza

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Patch

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..3283c77 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 +500,38 @@  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 = 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 = journal->j_flags &= ~JBD2_FROZEN;
+	write_unlock(&journal->j_state_lock);
+	smp_wmb();
+	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..31d6c23 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -835,6 +835,9 @@  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 +1016,11 @@  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) != JBD2_FROZEN))
 /*
  * Function declarations for the journaling transaction and buffer
  * management
@@ -1121,6 +1128,8 @@  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 *);