On Tue 20-12-22 23:05:51, Zhihao Cheng wrote:
> From: zhanchengbin <zhanchengbin1@xxxxxxxxxx>
>
> Following process will make data lost and could lead to a filesystem
> corrupted problem:
>
> 1. jh(bh) is inserted into T1->t_checkpoint_list, bh is dirty, and
> jh->b_transaction = NULL
> 2. T1 is added into journal->j_checkpoint_transactions.
> 3. Get bh prepare to write while doing checkpoing:
> PA PB
> do_get_write_access jbd2_log_do_checkpoint
> spin_lock(&jh->b_state_lock)
> if (buffer_dirty(bh))
> clear_buffer_dirty(bh) // clear buffer dirty
> set_buffer_jbddirty(bh)
> transaction =
> journal->j_checkpoint_transactions
> jh = transaction->t_checkpoint_list
> if (!buffer_dirty(bh))
> __jbd2_journal_remove_checkpoint(jh)
> // bh won't be flushed
> jbd2_cleanup_journal_tail
> __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved)
> 4. Aborting journal/Power-cut before writing latest bh on journal area.
>
> In this way we get a corrupted filesystem with bh'data lost.
>
> Fix it by wrapping clear_buffer_dirty(bh) and jh->b_transaction setting
> into journal->j_list_lock, so that jbd2_log_do_checkpoint() will wait
> until jh's new transaction fininshed even bh is currently not dirty.
>
> Cc: <stable@xxxxxxxxxx>
> Signed-off-by: zhanchengbin <zhanchengbin1@xxxxxxxxxx>
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
> ---
> This is a quick fix, I need some suggestions about this patch, whether
> it will import new problems if this patch is applied.
> Yi suggests that the formal solution could be splitting
> journal->j_list_lock into two locks: one protects checkpoint list and
> the other one for other lists. Besides, jh->b_state_lock should be
> held while traversing transaction->t_checkpoint_list in
> jbd2_log_do_checkpoint()/journal_shrink_one_cp_list().
>
> fs/jbd2/transaction.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
Good catch! Did you find it by code inspection or were you able to actually
trigger this problem?
I think there might be a simpler fix of the problem. Move the clearing
of buffer_dirty bit just before the call to __jbd2_journal_file_buffer().
We'll need to keep the buffer locked somewhat longer but that should not be
a huge deal.
Honza
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 6a404ac1c178..d22460001d6b 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -990,6 +990,7 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
> start_lock = jiffies;
> lock_buffer(bh);
> spin_lock(&jh->b_state_lock);
> + spin_lock(&journal->j_list_lock);
>
> /* If it takes too long to lock the buffer, trace it */
> time_lock = jbd2_time_diff(start_lock, jiffies);
> @@ -1039,6 +1040,7 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
>
> error = -EROFS;
> if (is_handle_aborted(handle)) {
> + spin_unlock(&journal->j_list_lock);
> spin_unlock(&jh->b_state_lock);
> goto out;
> }
> @@ -1049,8 +1051,10 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
> * b_next_transaction points to it
> */
> if (jh->b_transaction == transaction ||
> - jh->b_next_transaction == transaction)
> + jh->b_next_transaction == transaction) {
> + spin_unlock(&journal->j_list_lock);
> goto done;
> + }
>
> /*
> * this is the first time this transaction is touching this buffer,
> @@ -1073,11 +1077,11 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
> * Paired with barrier in jbd2_write_access_granted()
> */
> smp_wmb();
> - spin_lock(&journal->j_list_lock);
> __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
> spin_unlock(&journal->j_list_lock);
> goto done;
> }
> + spin_unlock(&journal->j_list_lock);
> /*
> * If there is already a copy-out version of this buffer, then we don't
> * need to make another one
> --
> 2.31.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
