From: Surbhi Palande Subject: Re: [PATCH v3] Adding support to freeze and unfreeze a journal Date: Wed, 11 May 2011 10:06:43 +0300 Message-ID: <4DCA3583.7010904@canonical.com> References: <4DC7F0E4.5070507@canonical.com> <1304952692-3858-1-git-send-email-surbhi.palande@canonical.com> <4DC806E9.1070806@redhat.com> Reply-To: surbhi.palande@canonical.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: jack@suse.cz, marco.stornelli@gmail.com, adilger.kernel@dilger.ca, toshi.okajima@jp.fujitsu.com, tytso@mit.edu, m.mizuma@jp.fujitsu.com, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Eric Sandeen Return-path: In-Reply-To: <4DC806E9.1070806@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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 >> --- >> 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 *); > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html