[Ocfs2-devel] [PATCH v2] ocfs2/journal: fix umount hang after flushing journal failure

[Gechangwei]

Hi,

As prior e-mail described, umount would hang after journal flushing failure.

When journal flushing in ocfs2_commit_cache() fails, following umount
procedure at stage of shutting journal may be blocked due to non-zero
transactions number.

Once jbd2_journal_flush() fails, the journal will be marked as ABORT
state within JBD2. There is no way to come back afterwards.

So there is no chance to set transactions number to zero, thus, shutting
journal may be blocked .

ocfs2_commit_thread()

    ocfs2_commit_cache()

        jbd2_journal_flush() -> failure takes journal into ABORT state,
thus, transaction number will never set to zero



The back trace is cited blow:

[<ffffffff8109de0c>] kthread_stop+0x4c/0x150
[<ffffffffc056a887>] ocfs2_journal_shutdown+0xa7/0x400 [ocfs2]
[<ffffffffc059fbde>] ocfs2_dismount_volume+0xbe/0x4a0 [ocfs2]
[<ffffffffc059fff7>] ocfs2_put_super+0x37/0xb0 [ocfs2]
[<ffffffff8120534e>] generic_shutdown_super+0x7e/0x110
[<ffffffff81205410>] kill_block_super+0x30/0x80
[<ffffffff81205669>] deactivate_locked_super+0x59/0x90
[<ffffffff812062ee>] deactivate_super+0x4e/0x70
[<ffffffff81222423>] cleanup_mnt+0x43/0x90
[<ffffffff812224c2>] __cleanup_mnt+0x12/0x20
[<ffffffff8109c247>] task_work_run+0xb7/0xf0
[<ffffffff81016f7c>] do_notify_resume+0x8c/0xa0
[<ffffffff817f8384>] int_signal+0x12/0x17
[<ffffffffffffffff>] 0xffffffffffffffff


To solve this issue, I propose an improved version of patch referring to
Andrew's and Joseph's  comments.

Any more comments is welcomed as always.


From f3315307dd2a30da138383340689a81708134a44 Mon Sep 17 00:00:00 2001
From: Changwei Ge <ge.changwei at h3c.com>
Date: Wed, 11 Jan 2017 09:05:35 +0800
Subject: [PATCH v2] fix umount hang after journal flushing failure

Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
---
 fs/ocfs2/journal.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
index a244f14..9a6b234 100644
--- a/fs/ocfs2/journal.c
+++ b/fs/ocfs2/journal.c
@@ -2315,6 +2315,24 @@ static int ocfs2_commit_thread(void *arg)
                             "commit_thread: %u transactions pending on "
                             "shutdown\n",
                             atomic_read(&journal->j_num_trans));
+
+                       if (status < 0) {
+                               mlog(ML_KTHREAD,
+                                    "Although %u transactions left,
journal must be shut down right now.\n",
+                                    atomic_read(&journal->j_num_trans));
+                               /*
+                                * This may a litte hacky, however, no
chance
+                                * for ocfs2/journal to decrease this
variable
+                                * thourgh commit-thread. I have to do so to
+                                * avoid umount hang after journal flushing
+                                * failure. Since jounral has been
marked ABORT
+                                * within jbd2_journal_flush, commit
cache will
+                                * never do any real work to flush
journal to
+                                * disk.Set t to ZERO so that umount will
+                                * continue during shutting downjournal
+                                */
+                               atomic_set(&journal->j_num_trans, 0);
+                       }
                }
        }

--
1.7.9.5


Thanks.

Br.

Changwei



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