jbd2: fix data missing when reusing bh which is ready to be checkpointed

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().

Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216898
Cc: <stable@kernel.org>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: zhanchengbin <zhanchengbin1@huawei.com>
Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230110015327.1181863-1-chengzhihao1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 6a404ac..15de138 100644 (file)
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1010,36 +1010,28 @@ repeat:
         * 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) {
+               warn_dirty_buffer(bh);
                /*
-                * 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);
-               }
-               /*
-                * 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);
+               /*
+                * The buffer is going to be added to BJ_Reserved list now and
+                * nothing guarantees jbd2_journal_dirty_metadata() will be
+                * ever called for it. So we need to set jbddirty bit here to
+                * make sure the buffer is dirtied and written out when the
+                * journaling machinery is done with it.
+                */
                set_buffer_jbddirty(bh);
        }
 
-       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 +1041,10 @@ repeat:
         * 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 +1068,24 @@ repeat:
                 */
                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