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Date:   Sun, 4 Jul 2021 10:04:21 -0400
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     Zhang Yi <yi.zhang@huawei.com>
Cc:     Jan Kara <jack@suse.cz>, linuxppc-dev@lists.ozlabs.org,
        Guoqing Jiang <guoqing.jiang@linux.dev>,
        Sachin Sant <sachinp@linux.vnet.ibm.com>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [powerpc][5.13.0-next-20210701] Kernel crash while running
 ltp(chdir01) tests
Message-ID: <YOG/5ZY1AL05jumi@mit.edu>
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 <4cc87ab3-aaa6-ed87-b690-5e5b99de8380@huawei.com>
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 <YN86yl5kgVaRixxQ@mit.edu>
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On Sat, Jul 03, 2021 at 12:55:09PM +0800, Zhang Yi wrote:
> Yeah, it sounds good to me. Do you want me to send the fix patch, or you
> modify your commit 8f9e16badb8fd in another email directly?

I've gone ahead and made the changes; what do you think?

I like how it also removes 40 lines of code.  :-)

     	  	    	     	      	   - Ted

From ef3130d1b0b8ca769252d6a722a2e59a00141383 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Fri, 2 Jul 2021 18:05:03 -0400
Subject: [PATCH] ext4: inline jbd2_journal_[un]register_shrinker()

The function jbd2_journal_unregister_shrinker() was getting called
twice when the file system was getting unmounted.  On Power and ARM
platforms this was causing kernel crash when unmounting the file
system, when a percpu_counter was destroyed twice.

Fix this by removing jbd2_journal_[un]register_shrinker() functions,
and inlining the shrinker setup and teardown into
journal_init_common() and jbd2_journal_destroy().  This means that
ext4 and ocfs2 now no longer need to know about registering and
unregistering jbd2's shrinker.

Also, while we're at it, rename the percpu counter from
j_jh_shrink_count to j_checkpoint_jh_count, since this makes it
clearer what this counter is intended to track.

Fixes: 4ba3fcdde7e3 ("jbd2,ext4: add a shrinker to release checkpointed buffers")
Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/super.c      |   8 ---
 fs/jbd2/checkpoint.c |   4 +-
 fs/jbd2/journal.c    | 148 +++++++++++++++++--------------------------
 include/linux/jbd2.h |   6 +-
 4 files changed, 63 insertions(+), 103 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b8ff0399e171..dfa09a277b56 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1184,7 +1184,6 @@ static void ext4_put_super(struct super_block *sb)
 	ext4_unregister_sysfs(sb);
 
 	if (sbi->s_journal) {
-		jbd2_journal_unregister_shrinker(sbi->s_journal);
 		aborted = is_journal_aborted(sbi->s_journal);
 		err = jbd2_journal_destroy(sbi->s_journal);
 		sbi->s_journal = NULL;
@@ -5176,7 +5175,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	sbi->s_ea_block_cache = NULL;
 
 	if (sbi->s_journal) {
-		jbd2_journal_unregister_shrinker(sbi->s_journal);
 		jbd2_journal_destroy(sbi->s_journal);
 		sbi->s_journal = NULL;
 	}
@@ -5502,12 +5500,6 @@ static int ext4_load_journal(struct super_block *sb,
 		ext4_commit_super(sb);
 	}
 
-	err = jbd2_journal_register_shrinker(journal);
-	if (err) {
-		EXT4_SB(sb)->s_journal = NULL;
-		goto err_out;
-	}
-
 	return 0;
 
 err_out:
diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 51d1eb2ffeb9..746132998c57 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -701,7 +701,7 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
 
 	__buffer_unlink(jh);
 	jh->b_cp_transaction = NULL;
-	percpu_counter_dec(&journal->j_jh_shrink_count);
+	percpu_counter_dec(&journal->j_checkpoint_jh_count);
 	jbd2_journal_put_journal_head(jh);
 
 	/* Is this transaction empty? */
@@ -764,7 +764,7 @@ void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
 		jh->b_cpnext->b_cpprev = jh;
 	}
 	transaction->t_checkpoint_list = jh;
-	percpu_counter_inc(&transaction->t_journal->j_jh_shrink_count);
+	percpu_counter_inc(&transaction->t_journal->j_checkpoint_jh_count);
 }
 
 /*
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 152880c298ca..8a9c94dd3599 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1283,6 +1283,48 @@ static int jbd2_min_tag_size(void)
 	return sizeof(journal_block_tag_t) - 4;
 }
 
+/**
+ * jbd2_journal_shrink_scan()
+ *
+ * Scan the checkpointed buffer on the checkpoint list and release the
+ * journal_head.
+ */
+static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
+					      struct shrink_control *sc)
+{
+	journal_t *journal = container_of(shrink, journal_t, j_shrinker);
+	unsigned long nr_to_scan = sc->nr_to_scan;
+	unsigned long nr_shrunk;
+	unsigned long count;
+
+	count = percpu_counter_read_positive(&journal->j_checkpoint_jh_count);
+	trace_jbd2_shrink_scan_enter(journal, sc->nr_to_scan, count);
+
+	nr_shrunk = jbd2_journal_shrink_checkpoint_list(journal, &nr_to_scan);
+
+	count = percpu_counter_read_positive(&journal->j_checkpoint_jh_count);
+	trace_jbd2_shrink_scan_exit(journal, nr_to_scan, nr_shrunk, count);
+
+	return nr_shrunk;
+}
+
+/**
+ * jbd2_journal_shrink_count()
+ *
+ * Count the number of checkpoint buffers on the checkpoint list.
+ */
+static unsigned long jbd2_journal_shrink_count(struct shrinker *shrink,
+					       struct shrink_control *sc)
+{
+	journal_t *journal = container_of(shrink, journal_t, j_shrinker);
+	unsigned long count;
+
+	count = percpu_counter_read_positive(&journal->j_checkpoint_jh_count);
+	trace_jbd2_shrink_count(journal, sc->nr_to_scan, count);
+
+	return count;
+}
+
 /*
  * Management for journal control blocks: functions to create and
  * destroy journal_t structures, and to initialise and read existing
@@ -1361,6 +1403,19 @@ static journal_t *journal_init_common(struct block_device *bdev,
 	journal->j_sb_buffer = bh;
 	journal->j_superblock = (journal_superblock_t *)bh->b_data;
 
+	journal->j_shrink_transaction = NULL;
+	journal->j_shrinker.scan_objects = jbd2_journal_shrink_scan;
+	journal->j_shrinker.count_objects = jbd2_journal_shrink_count;
+	journal->j_shrinker.seeks = DEFAULT_SEEKS;
+	journal->j_shrinker.batch = journal->j_max_transaction_buffers;
+
+	if (percpu_counter_init(&journal->j_checkpoint_jh_count, 0, GFP_KERNEL))
+		goto err_cleanup;
+
+	if (register_shrinker(&journal->j_shrinker)) {
+		percpu_counter_destroy(&journal->j_checkpoint_jh_count);
+		goto err_cleanup;
+	}
 	return journal;
 
 err_cleanup:
@@ -2050,93 +2105,6 @@ int jbd2_journal_load(journal_t *journal)
 	return -EIO;
 }
 
-/**
- * jbd2_journal_shrink_scan()
- *
- * Scan the checkpointed buffer on the checkpoint list and release the
- * journal_head.
- */
-static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
-					      struct shrink_control *sc)
-{
-	journal_t *journal = container_of(shrink, journal_t, j_shrinker);
-	unsigned long nr_to_scan = sc->nr_to_scan;
-	unsigned long nr_shrunk;
-	unsigned long count;
-
-	count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
-	trace_jbd2_shrink_scan_enter(journal, sc->nr_to_scan, count);
-
-	nr_shrunk = jbd2_journal_shrink_checkpoint_list(journal, &nr_to_scan);
-
-	count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
-	trace_jbd2_shrink_scan_exit(journal, nr_to_scan, nr_shrunk, count);
-
-	return nr_shrunk;
-}
-
-/**
- * jbd2_journal_shrink_count()
- *
- * Count the number of checkpoint buffers on the checkpoint list.
- */
-static unsigned long jbd2_journal_shrink_count(struct shrinker *shrink,
-					       struct shrink_control *sc)
-{
-	journal_t *journal = container_of(shrink, journal_t, j_shrinker);
-	unsigned long count;
-
-	count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
-	trace_jbd2_shrink_count(journal, sc->nr_to_scan, count);
-
-	return count;
-}
-
-/**
- * jbd2_journal_register_shrinker()
- * @journal: Journal to act on.
- *
- * Init a percpu counter to record the checkpointed buffers on the checkpoint
- * list and register a shrinker to release their journal_head.
- */
-int jbd2_journal_register_shrinker(journal_t *journal)
-{
-	int err;
-
-	journal->j_shrink_transaction = NULL;
-
-	err = percpu_counter_init(&journal->j_jh_shrink_count, 0, GFP_KERNEL);
-	if (err)
-		return err;
-
-	journal->j_shrinker.scan_objects = jbd2_journal_shrink_scan;
-	journal->j_shrinker.count_objects = jbd2_journal_shrink_count;
-	journal->j_shrinker.seeks = DEFAULT_SEEKS;
-	journal->j_shrinker.batch = journal->j_max_transaction_buffers;
-
-	err = register_shrinker(&journal->j_shrinker);
-	if (err) {
-		percpu_counter_destroy(&journal->j_jh_shrink_count);
-		return err;
-	}
-
-	return 0;
-}
-EXPORT_SYMBOL(jbd2_journal_register_shrinker);
-
-/**
- * jbd2_journal_unregister_shrinker()
- * @journal: Journal to act on.
- *
- * Unregister the checkpointed buffer shrinker and destroy the percpu counter.
- */
-void jbd2_journal_unregister_shrinker(journal_t *journal)
-{
-	percpu_counter_destroy(&journal->j_jh_shrink_count);
-	unregister_shrinker(&journal->j_shrinker);
-}
-EXPORT_SYMBOL(jbd2_journal_unregister_shrinker);
-
 /**
  * jbd2_journal_destroy() - Release a journal_t structure.
  * @journal: Journal to act on.
@@ -2209,8 +2177,10 @@ int jbd2_journal_destroy(journal_t *journal)
 		brelse(journal->j_sb_buffer);
 	}
 
-	jbd2_journal_unregister_shrinker(journal);
-
+	if (journal->j_shrinker.flags & SHRINKER_REGISTERED) {
+		percpu_counter_destroy(&journal->j_checkpoint_jh_count);
+		unregister_shrinker(&journal->j_shrinker);
+	}
 	if (journal->j_proc_entry)
 		jbd2_stats_proc_exit(journal);
 	iput(journal->j_inode);
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 6cc035321562..fd933c45281a 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -918,11 +918,11 @@ struct journal_s
 	struct shrinker		j_shrinker;
 
 	/**
-	 * @j_jh_shrink_count:
+	 * @j_checkpoint_jh_count:
 	 *
 	 * Number of journal buffers on the checkpoint list. [j_list_lock]
 	 */
-	struct percpu_counter	j_jh_shrink_count;
+	struct percpu_counter	j_checkpoint_jh_count;
 
 	/**
 	 * @j_shrink_transaction:
@@ -1556,8 +1556,6 @@ extern int	   jbd2_journal_set_features
 		   (journal_t *, unsigned long, unsigned long, unsigned long);
 extern void	   jbd2_journal_clear_features
 		   (journal_t *, unsigned long, unsigned long, unsigned long);
-extern int	   jbd2_journal_register_shrinker(journal_t *journal);
-extern void	   jbd2_journal_unregister_shrinker(journal_t *journal);
 extern int	   jbd2_journal_load       (journal_t *journal);
 extern int	   jbd2_journal_destroy    (journal_t *);
 extern int	   jbd2_journal_recover    (journal_t *journal);
-- 
2.31.0