Date: Fri, 27 Nov 2015 05:23:13 +0000 (GMT)
From: Daeho Jeong <daeho.jeong@samsung.com>
Subject: Re: [PATCH 3.2 16/52] ext4,
 jbd2: ensure entering into panic after recording an error in superblock
To: Ben Hutchings <ben@decadent.org.uk>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Cc: "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "Theodore Ts'o" <tytso@mit.edu>,
        =?utf-8?Q?=EC=9A=B0=ED=98=B8=EB=B9=88?= <hobin.woo@samsung.com>,
        =?utf-8?Q?=EC=A0=95=EB=8C=80=ED=98=B8?= <daeho.jeong@samsung.com>
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It looks good. Thank you. :-)

------- Original Message -------
Sender : Ben Hutchings<ben@decadent.org.uk>
Date : 2015-11-25 07:33 (GMT+09:00)
Title : [PATCH 3.2 16/52] ext4, jbd2: ensure entering into panic after recording an error in superblock

3.2.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Daeho Jeong 

commit 4327ba52afd03fc4b5afa0ee1d774c9c5b0e85c5 upstream.

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 occurred 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 
Signed-off-by: Daeho Jeong 
Signed-off-by: Theodore Ts'o 
Signed-off-by: Ben Hutchings 
---
fs/ext4/super.c      | 12 ++++++++++--
fs/jbd2/journal.c    |  6 +++++-
include/linux/jbd2.h |  1 +
3 files changed, 16 insertions(+), 3 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -463,9 +463,13 @@ static void ext4_handle_error(struct sup
ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
sb->s_flags |= MS_RDONLY;
}
- if (test_opt(sb, ERRORS_PANIC))
+ if (test_opt(sb, ERRORS_PANIC)) {
+ if (EXT4_SB(sb)->s_journal &&
+   !(EXT4_SB(sb)->s_journal->j_flags & JBD2_REC_ERR))
+ return;
panic("EXT4-fs (device %s): panic forced after error\n",
sb->s_id);
+ }
}

void __ext4_error(struct super_block *sb, const char *function,
@@ -628,8 +632,12 @@ void __ext4_abort(struct super_block *sb
jbd2_journal_abort(EXT4_SB(sb)->s_journal, -EIO);
save_error_info(sb, function, line);
}
- if (test_opt(sb, ERRORS_PANIC))
+ if (test_opt(sb, ERRORS_PANIC)) {
+ if (EXT4_SB(sb)->s_journal &&
+   !(EXT4_SB(sb)->s_journal->j_flags & JBD2_REC_ERR))
+ return;
panic("EXT4-fs panic from previous error\n");
+ }
}

void ext4_msg(struct super_block *sb, const char *prefix, const char *fmt, ...)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1956,8 +1956,12 @@ static void __journal_abort_soft (journa

__jbd2_journal_abort_hard(journal);

- if (errno)
+ if (errno) {
jbd2_journal_update_sb_errno(journal);
+ write_lock(&journal->j_state_lock);
+ journal->j_flags |= JBD2_REC_ERR;
+ write_unlock(&journal->j_state_lock);
+ }
}

/**
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -954,6 +954,7 @@ struct journal_s
#define JBD2_ABORT_ON_SYNCDATA_ERR 0x040 /* Abort the journal on file
* data write error in ordered
* mode */
+#define JBD2_REC_ERR 0x080 /* The errno in the sb has been recorded */

/*
  * Function declarations for the journaling transaction and buffer????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m????????????I?