[PATCH -v2] ext4: inline jbd2_journal_[un]register_shrinker()

Theodore Ts'o
2021-07-05T14:51:11Z

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: Jon Hunter <jonathanh@nvidia.com>
Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/super.c | 8 ---
fs/jbd2/checkpoint.c | 4 +-
fs/jbd2/journal.c | 149 +++++++++++++++++--------------------------
include/linux/jbd2.h | 6 +-
4 files changed, 64 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..35302bc192eb 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
@@ -1361,9 +1403,23 @@ 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:
+ brelse(journal->j_sb_buffer);
kfree(journal->j_wbuf);
jbd2_journal_destroy_revoke(journal);
kfree(journal);
@@ -2050,93 +2106,6 @@ 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 +2178,10 @@ 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