From: Andreas Dilger Subject: Re: [PATCH v3] Adding support to freeze and unfreeze a journal Date: Wed, 11 May 2011 03:05:54 -0600 Message-ID: <93775CC9-ACDF-4AD4-96C3-F791679008EE@dilger.ca> References: <4DC7F0E4.5070507@canonical.com> <1304952692-3858-1-git-send-email-surbhi.palande@canonical.com> <4DC806E9.1070806@redhat.com> <4DCA3583.7010904@canonical.com> Mime-Version: 1.0 (iPhone Mail 8H7) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT Cc: Eric Sandeen , "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: "surbhi.palande@canonical.com" Return-path: Received: from smtp.resortinternet.net ([65.114.208.136]:60201 "EHLO smtp.resortinternet.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750815Ab1EKXuz convert rfc822-to-8bit (ORCPT ); Wed, 11 May 2011 19:50:55 -0400 In-Reply-To: <4DCA3583.7010904@canonical.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2011-05-11, at 1:06 AM, Surbhi Palande 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 >>> --- >>> 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 >