Re: [powerpc][5.13.0-next-20210701] Kernel crash while running ltp(chdir01) tests

Theodore Ts'o
2021-07-02T22:12:12Z

On Fri, Jul 02, 2021 at 12:11:54PM -0400, Theodore Ts'o wrote:
> So it probably makes more sense to keep jbd2_journal_unregister_shrinker()
> in jbd2_destroy_journal(), since arguably the fact that we are using a
> shrinker is an internal implementation detail, and the users of jbd2
> ideally shouldn't need to be expected to know they have unregister
> jbd2's shirnkers.
>
> Similarly, perhaps we should be moving jbd2_journal_register_shirnker()
> into jbd2_journal_init_common(). We can un-export the register and
> unshrink register functions, and declare them as static functions internal
> to fs/jbd2/journal.c.
>
> What do you think?

Like this...

commit 8f9e16badb8fda3391e03146a47c93e76680efaf
Author: Theodore Ts'o <tytso@mit.edu>
Date: Fri Jul 2 18:05:03 2021 -0400

ext4: fix doubled call to jbd2_journal_unregister_shrinker()

On Power and ARM platforms this was causing kernel crash when
unmounting the file system, due to a percpu_counter getting destroyed
twice.

Fix this by cleaning how the jbd2 shrinker is initialized and
uninitiazed by making it solely the responsibility of
fs/jbd2/journal.c.

Fixes: 4ba3fcdde7e3 ("jbd2,ext4: add a shrinker to release checkpointed buffers")
Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

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/journal.c b/fs/jbd2/journal.c
index 152880c298ca..2595703aca51 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -99,6 +99,8 @@ EXPORT_SYMBOL(jbd2_journal_begin_ordered_truncate);
EXPORT_SYMBOL(jbd2_inode_cache);

static int jbd2_journal_create_slab(size_t slab_size);
+static int jbd2_journal_register_shrinker(journal_t *journal);
+static void jbd2_journal_unregister_shrinker(journal_t *journal);

#ifdef CONFIG_JBD2_DEBUG
void __jbd2_debug(int level, const char *file, const char *func,
@@ -2043,7 +2045,8 @@ int jbd2_journal_load(journal_t *journal)
goto recovery_error;

journal->j_flags |= JBD2_LOADED;
- return 0;
+
+ return jbd2_journal_register_shrinker(journal);

recovery_error:
printk(KERN_WARNING "JBD2: recovery failed\n");
@@ -2099,7 +2102,7 @@ static unsigned long jbd2_journal_shrink_count(struct shrinker *shrink,
* 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)
+static int jbd2_journal_register_shrinker(journal_t *journal)
{
int err;

@@ -2122,7 +2125,6 @@ int jbd2_journal_register_shrinker(journal_t *journal)

return 0;
}
-EXPORT_SYMBOL(jbd2_journal_register_shrinker);

/**
* jbd2_journal_unregister_shrinker()
@@ -2130,12 +2132,13 @@ EXPORT_SYMBOL(jbd2_journal_register_shrinker);
*
* Unregister the checkpointed buffer shrinker and destroy the percpu counter.
*/
-void jbd2_journal_unregister_shrinker(journal_t *journal)
+static void jbd2_journal_unregister_shrinker(journal_t *journal)
{
- percpu_counter_destroy(&journal->j_jh_shrink_count);
- unregister_shrinker(&journal->j_shrinker);
+ if (journal->j_shrinker.flags & SHRINKER_REGISTERED) {
+ 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.
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 6cc035321562..632afbe4b18f 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -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);