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

On 2021/7/3 0:11, Theodore Ts'o wrote:

On Fri, Jul 02, 2021 at 09:52:13PM +0800, Zhang Yi wrote:

quoted

Sorry about not catching this problem, this fix is not format corrected,
if you think this fix is OK, I can send a patch after test.

The issue I see with your approach, which removes the
jbd2_journal_unregister_shrinker() call from jbd2_destsroy_journal(),
is that means that *all* callers of jbd2_destroy_journal now have to
be responsible for calling jbd2_journal_unregister_shrinker() --- and
there a number of call sites to jbd2_journal_unregister_shrinker():

fs/ext4/super.c:		err = jbd2_journal_destroy(sbi->s_journal);
fs/ext4/super.c:		jbd2_journal_destroy(sbi->s_journal);
fs/ext4/super.c:	jbd2_journal_destroy(journal);
fs/ext4/super.c:		jbd2_journal_destroy(journal);
fs/ext4/super.c:	jbd2_journal_destroy(journal);
fs/ocfs2/journal.c:	if (!jbd2_journal_destroy(journal->j_journal) && !status) {
fs/ocfs2/journal.c:		jbd2_journal_destroy(journal);
fs/ocfs2/journal.c:	jbd2_journal_destroy(journal);

Originally, I want to add this shrinker as a optional feature for jbd2 because
only ext4 use it now and I'm not sure does ocfs2 needs this feature. So I export
jbd2_journal_[un]register_shrinker(), ext4 could invoke them individually.

If with my fix, there is no responsible for calling
jbd2_journal_unregister_shrinker() before every jbd2_journal_destroy(). There
are only two places that need to do this, one is the error path after
ext4_load_journal() because we have already register the shrinker, other one
is in ext4_put_super() before the final release of the journal.
jbd2_journal_unregister_shrinker() and jbd2_journal_destroy() do not have
the strong dependence.

And one more thing we to could do is rename the 'j_jh_shrink_count' to something
like 'j_checkpoint_jh_count' because we always init it no matter we register the
shrinker or not later.

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.

Yeah, it's make sense and It's sound good to me if the shrinker doesn't have
side effects on osfs2.

Thanks,
Yi.