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Fri, 19 Jul 2024 23:24:03 -0700 (PDT) Received: from localhost.localdomain ([163.53.18.10]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2ccf7c76fe7sm2755125a91.33.2024.07.19.23.24.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jul 2024 23:24:03 -0700 (PDT) From: zhangshida X-Google-Original-From: zhangshida To: tytso@mit.edu, jack@suse.com Cc: linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, zhangshida@kylinos.cn, starzhangzsd@gmail.com, Baolin Liu Subject: [RFC PATCH] jbd2: fix a potential assertion failure due to improperly dirtied buffer Date: Sat, 20 Jul 2024 14:23:56 +0800 Message-Id: <20240720062356.2522658-1-zhangshida@kylinos.cn> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Shida Zhang On an old kernel version(4.19, ext3, journal=data, pagesize=64k), an assertion failure will occasionally be triggered by the line below: jbd2_journal_commit_transaction { ... J_ASSERT_BH(bh, !buffer_dirty(bh)); /* * The buffer on BJ_Forget list and not jbddirty means ... } AFAIC, that's how the problem works: -------- journal_unmap_buffer jbd2_journal_invalidatepage __ext4_journalled_invalidatepage ext4_journalled_invalidatepage do_invalidatepage truncate_inode_pages_range truncate_inode_pages truncate_pagecache ext4_setattr -------- First try to truncate and invalidate the page. Sometimes the buffer and the page won't be freed immediately. the buffer will be sent to the BJ_Forget list of the currently committing transaction. Maybe the transaction knows when and how to free the buffer better. The buffer's states now: !jbd_dirty !mapped !dirty Then jbd2_journal_commit_transaction(）will try to iterate over the BJ_Forget list: -------- jbd2_journal_commit_transaction() while (commit_transaction->t_forget) { ... } -------- At this exact moment, another write comes: -------- mark_buffer_dirty __block_write_begin_int __block_write_begin ext4_write_begin -------- it sees a unmapped new buffer, and marks it as dirty. Finally, jbd2_journal_commit_transaction(）will trip over the assertion during the BJ_Forget list iteration. After an code analysis, it seems that nothing can prevent the __block_write_begin() from dirtying the buffer at this very moment. The same condition may also be applied to the lattest kernel version. To fix it: Add some checks to see if it is the case dirtied by __block_write_begin(). if yes, it's okay and just let it go. The one who dirtied it and the jbd2_journal_commit_transaction() will know how to cooperate together and deal with it in a proper manner. if no, try to complain as we normally will do. Reported-by: Baolin Liu Signed-off-by: Shida Zhang --- fs/jbd2/commit.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c index 75ea4e9a5cab..2c13d0af92d8 100644 --- a/fs/jbd2/commit.c +++ b/fs/jbd2/commit.c @@ -1023,7 +1023,20 @@ void jbd2_journal_commit_transaction(journal_t *journal) if (is_journal_aborted(journal)) clear_buffer_jbddirty(bh); } else { - J_ASSERT_BH(bh, !buffer_dirty(bh)); + bool try_to_complain = 1; + struct folio *folio = NULL; + + folio = bh->b_folio; + /* + * Try not to complain about the dirty buffer marked dirty + * by __block_write_begin(). + */ + if (buffer_dirty(bh) && folio && folio->mapping + && folio_test_locked(folio)) + try_to_complain = 0; + + if (try_to_complain) + J_ASSERT_BH(bh, !buffer_dirty(bh)); /* * The buffer on BJ_Forget list and not jbddirty means * it has been freed by this transaction and hence it