linux-ext4 - [PATCH] ext4, jbd2: ensure entering into panic after recording an error in JBD2 superblock

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Date:	Mon, 10 Aug 2015 05:44:49 +0000 (GMT)
From:	Daeho Jeong <daeho.jeong@...sung.com>
To:	"tytso@....edu" <tytso@....edu>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Cc:	"daehojng@...il.com" <daehojng@...il.com>,
	정대호 <daeho.jeong@...sung.com>
Subject: [PATCH] ext4, jbd2: ensure entering into panic after recording an
 error in JBD2 superblock

If a EXT4 filesystem utilizes JBD2 journaling and an error occurs, the journaling
will be aborted first and the error number will be recorded into JBD2 superblock
and, finally, the system will enter into the panic state in "errors=panic" option.
But, in the rare case, this sequence is little twisted like the below figure and
it will happen that the system enters into panic state, which means the system
reset in mobile environment, before completion of recording an error in the
journal superblock. In this case, e2fsck cannot recognize that the filesystem
failure occured in the previous run and the corruption wouldn't be fixed.

Task A                                                 Task B
ext4_handle_error()
-> jbd2_journal_abort()
  -> __journal_abort_soft()
    -> __jbd2_journal_abort_hard()
    | -> journal->j_flags |= JBD2_ABORT;
    |                                                      __ext4_abort()
    |                                                      -> jbd2_journal_abort()
    |                                                      | -> __journal_abort_soft()
    |                                                      |   -> if (journal->j_flags & JBD2_ABORT)
    |                                                      |           return;
    |                                                      -> panic()
    -> jbd2_journal_update_sb_errno()

Tested-by: Hobin Woo <hobin.woo@...sung.com>
Signed-off-by: Daeho Jeong <daeho.jeong@...sung.com>
Signed-off-by: Youngjin Gil <youngjin.gil@...sung.com>
---
 fs/jbd2/journal.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index b96bd80..b265fd8 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -2051,10 +2051,10 @@ static void __journal_abort_soft (journal_t *journal, int errno)
        if (!journal->j_errno)
                journal->j_errno = errno;

-       __jbd2_journal_abort_hard(journal);
-
        if (errno)
                jbd2_journal_update_sb_errno(journal);
+
+       __jbd2_journal_abort_hard(journal);
 }

 /**