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Date: Fri, 6 Jan 2023 15:22:55 +0100
From: Jan Kara <jack@...e.cz>
To: Zhihao Cheng <chengzhihao1@...wei.com>
Cc: tytso@....edu, jack@...e.com, linux-ext4@...r.kernel.org,
linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
libaokun1@...wei.com, zhanchengbin1@...wei.com
Subject: Re: [PATCH v2] jbd2: Fix data missing when reusing bh which is ready
to be checkpointed
On Fri 06-01-23 19:56:03, Zhihao Cheng wrote:
> 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's data lost.
>
> Fix it by moving the clearing of buffer_dirty bit just before the call
> to __jbd2_journal_file_buffer(), both bit clearing and jh->b_transaction
> assignment are under journal->j_list_lock locked, so that
> jbd2_log_do_checkpoint() will wait until jh's new transaction fininshed
> even bh is currently not dirty. And journal_shrink_one_cp_list() won't
> remove jh from checkpoint list if the buffer head is reused in
> do_get_write_access().
>
> Cc: <stable@...nel.org>
> Signed-off-by: Zhihao Cheng <chengzhihao1@...wei.com>
> Signed-off-by: zhanchengbin <zhanchengbin1@...wei.com>
> Suggested-by: Jan Kara <jack@...e.cz>
Thanks for the patch! It looks good, some suggestions for making it a bit
more tidy below:
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 6a404ac1c178..06a5e7961ef2 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -1010,36 +1010,37 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
> * ie. locked but not dirty) or tune2fs (which may actually have
> * the buffer dirtied, ugh.) */
>
> - if (buffer_dirty(bh)) {
> + if (buffer_dirty(bh) && jh->b_transaction) {
> /*
> * First question: is this buffer already part of the current
> * transaction or the existing committing transaction?
> */
> - if (jh->b_transaction) {
> - J_ASSERT_JH(jh,
> - jh->b_transaction == transaction ||
> - jh->b_transaction ==
> - journal->j_committing_transaction);
> - if (jh->b_next_transaction)
> - J_ASSERT_JH(jh, jh->b_next_transaction ==
> - transaction);
> - warn_dirty_buffer(bh);
> - }
> + J_ASSERT_JH(jh, jh->b_transaction == transaction ||
> + jh->b_transaction == journal->j_committing_transaction);
> + if (jh->b_next_transaction)
> + J_ASSERT_JH(jh, jh->b_next_transaction == transaction);
> + warn_dirty_buffer(bh);
> /*
> - * In any case we need to clean the dirty flag and we must
> - * do it under the buffer lock to be sure we don't race
> - * with running write-out.
> + * We need to clean the dirty flag and we must do it under the
> + * buffer lock to be sure we don't race with running write-out.
> */
> JBUFFER_TRACE(jh, "Journalling dirty buffer");
> clear_buffer_dirty(bh);
> + /*
> + * Setting jbddirty after clearing buffer dirty is necessary.
> + * Function jbd2_journal_restart() could keep buffer on
> + * BJ_Reserved list until the transaction committing, then the
> + * buffer won't be dirtied by jbd2_journal_refile_buffer()
> + * after committing, the buffer couldn't fall on disk even
> + * last checkpoint finished, which may corrupt filesystem.
> + */
> set_buffer_jbddirty(bh);
> }
So I think the sequence:
if (buffer_dirty(bh)) {
warn_dirty_buffer(bh);
JBUFFER_TRACE(jh, "Journalling dirty buffer");
clear_buffer_dirty(bh);
set_buffer_jbddirty(bh);
}
can be moved into the branch
if (jh->b_transaction == transaction ||
jh->b_next_transaction == transaction) {
below. That way you can drop the assertions as well because they happen
later in do_get_write_access() again anyway.
Also I don't quite understand the new comment you have added. Do you mean
we need to not only clear BH_Dirty bit but also set BH_JBDdirty as dirtying
(through jbd2_journal_dirty_metadata()) does not have to follow after
do_get_write_access()?
Otherwise the patch looks good.
Honza
>
> - unlock_buffer(bh);
> -
> error = -EROFS;
> if (is_handle_aborted(handle)) {
> spin_unlock(&jh->b_state_lock);
> + unlock_buffer(bh);
> goto out;
> }
> error = 0;
> @@ -1049,8 +1050,10 @@ 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) {
> + unlock_buffer(bh);
> goto done;
> + }
>
> /*
> * this is the first time this transaction is touching this buffer,
> @@ -1074,10 +1077,24 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
> */
> smp_wmb();
> spin_lock(&journal->j_list_lock);
> + if (test_clear_buffer_dirty(bh)) {
> + /*
> + * Execute buffer dirty clearing and jh->b_transaction
> + * assignment under journal->j_list_lock locked to
> + * prevent bh being removed from checkpoint list if
> + * the buffer is in an intermediate state (not dirty
> + * and jh->b_transaction is NULL).
> + */
> + JBUFFER_TRACE(jh, "Journalling dirty buffer");
> + set_buffer_jbddirty(bh);
> + }
> __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
> spin_unlock(&journal->j_list_lock);
> + unlock_buffer(bh);
> goto done;
> }
> + unlock_buffer(bh);
> +
> /*
> * 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@...e.com>
SUSE Labs, CR
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