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Date: Tue, 9 Jun 2020 13:50:26 +0200
From: Jan Kara <jack@...e.cz>
To: "zhangyi (F)" <yi.zhang@...wei.com>
Cc: linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
adilger.kernel@...ger.ca, zhangxiaoxu5@...wei.com
Subject: Re: [PATCH v2] ext4, jbd2: ensure panic by fix a race between jbd2
abort and ext4 error handlers
On Tue 09-06-20 15:35:40, zhangyi (F) wrote:
> In the ext4 filesystem with errors=panic, if one process is recording
> errno in the superblock when invoking jbd2_journal_abort() due to some
> error cases, it could be raced by another __ext4_abort() which is
> setting the SB_RDONLY flag but missing panic because errno has not been
> recorded.
>
> jbd2_journal_commit_transaction()
> jbd2_journal_abort()
> journal->j_flags |= JBD2_ABORT;
> jbd2_journal_update_sb_errno()
> | ext4_journal_check_start()
> | __ext4_abort()
> | sb->s_flags |= SB_RDONLY;
> | if (!JBD2_REC_ERR)
> | return;
> journal->j_flags |= JBD2_REC_ERR;
>
> Finally, it will no longer trigger panic because the filesystem has
> already been set read-only. Fix this by introduce j_abort_mutex to make
> sure journal abort is completed before panic, and remove JBD2_REC_ERR
> flag.
>
> Fixes: 4327ba52afd03 ("ext4, jbd2: ensure entering into panic after recording an error in superblock")
> Signed-off-by: zhangyi (F) <yi.zhang@...wei.com>
> Cc: <stable@...r.kernel.org>
Great, thanks! The patch looks good to me. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
> ---
> v1 -> v2:
> - Introduce j_abort_mutex and remove j_record_errno completion.
>
> fs/ext4/super.c | 16 +++++-----------
> fs/jbd2/journal.c | 17 ++++++++++++-----
> include/linux/jbd2.h | 6 +++++-
> 3 files changed, 22 insertions(+), 17 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 9824cd8203e8..8b3771e61c49 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -522,9 +522,6 @@ static void ext4_handle_error(struct super_block *sb)
> smp_wmb();
> sb->s_flags |= SB_RDONLY;
> } else 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);
> }
> @@ -725,23 +722,20 @@ void __ext4_abort(struct super_block *sb, const char *function,
> va_end(args);
>
> if (sb_rdonly(sb) == 0) {
> - ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
> EXT4_SB(sb)->s_mount_flags |= EXT4_MF_FS_ABORTED;
> + if (EXT4_SB(sb)->s_journal)
> + jbd2_journal_abort(EXT4_SB(sb)->s_journal, -EIO);
> +
> + ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
> /*
> * Make sure updated value of ->s_mount_flags will be visible
> * before ->s_flags update
> */
> smp_wmb();
> sb->s_flags |= SB_RDONLY;
> - if (EXT4_SB(sb)->s_journal)
> - jbd2_journal_abort(EXT4_SB(sb)->s_journal, -EIO);
> }
> - if (test_opt(sb, ERRORS_PANIC) && !system_going_down()) {
> - if (EXT4_SB(sb)->s_journal &&
> - !(EXT4_SB(sb)->s_journal->j_flags & JBD2_REC_ERR))
> - return;
> + if (test_opt(sb, ERRORS_PANIC) && !system_going_down())
> panic("EXT4-fs panic from previous error\n");
> - }
> }
>
> void __ext4_msg(struct super_block *sb,
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index a49d0e670ddf..e4944436e733 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1140,6 +1140,7 @@ static journal_t *journal_init_common(struct block_device *bdev,
> init_waitqueue_head(&journal->j_wait_commit);
> init_waitqueue_head(&journal->j_wait_updates);
> init_waitqueue_head(&journal->j_wait_reserved);
> + mutex_init(&journal->j_abort_mutex);
> mutex_init(&journal->j_barrier);
> mutex_init(&journal->j_checkpoint_mutex);
> spin_lock_init(&journal->j_revoke_lock);
> @@ -1402,7 +1403,8 @@ static int jbd2_write_superblock(journal_t *journal, int write_flags)
> printk(KERN_ERR "JBD2: Error %d detected when updating "
> "journal superblock for %s.\n", ret,
> journal->j_devname);
> - jbd2_journal_abort(journal, ret);
> + if (!is_journal_aborted(journal))
> + jbd2_journal_abort(journal, ret);
> }
>
> return ret;
> @@ -2153,6 +2155,13 @@ void jbd2_journal_abort(journal_t *journal, int errno)
> {
> transaction_t *transaction;
>
> + /*
> + * Lock the aborting procedure until everything is done, this avoid
> + * races between filesystem's error handling flow (e.g. ext4_abort()),
> + * ensure panic after the error info is written into journal's
> + * superblock.
> + */
> + mutex_lock(&journal->j_abort_mutex);
> /*
> * ESHUTDOWN always takes precedence because a file system check
> * caused by any other journal abort error is not required after
> @@ -2167,6 +2176,7 @@ void jbd2_journal_abort(journal_t *journal, int errno)
> journal->j_errno = errno;
> jbd2_journal_update_sb_errno(journal);
> }
> + mutex_unlock(&journal->j_abort_mutex);
> return;
> }
>
> @@ -2188,10 +2198,7 @@ void jbd2_journal_abort(journal_t *journal, int errno)
> * layer could realise that a filesystem check is needed.
> */
> jbd2_journal_update_sb_errno(journal);
> -
> - write_lock(&journal->j_state_lock);
> - journal->j_flags |= JBD2_REC_ERR;
> - write_unlock(&journal->j_state_lock);
> + mutex_unlock(&journal->j_abort_mutex);
> }
>
> /**
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index f613d8529863..d56128df2aff 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -765,6 +765,11 @@ struct journal_s
> */
> int j_errno;
>
> + /**
> + * @j_abort_mutex: Lock the whole aborting procedure.
> + */
> + struct mutex j_abort_mutex;
> +
> /**
> * @j_sb_buffer: The first part of the superblock buffer.
> */
> @@ -1247,7 +1252,6 @@ JBD2_FEATURE_INCOMPAT_FUNCS(csum3, CSUM_V3)
> #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
> --
> 2.25.4
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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