From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-119.freemail.mail.aliyun.com (out30-119.freemail.mail.aliyun.com [115.124.30.119]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 435EE3B960F for ; Mon, 29 Jun 2026 11:38:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.119 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782733123; cv=none; b=duhfugg0OccVQENBhVpjo3FBmTJ2fi8b1V9apPfqBjpPhv4Hxt9+x35HEsFmxICi3Z7MiWwfcyQvcIJvsV6YjXbC6fKDT4rIQWT00caUTOE51HIIfU3D9ieZH+q8sUsK0ZbOzoJM9DwBPamnnVGGiZK5gKvC2V9UPuNOAqh7UGk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782733123; c=relaxed/simple; bh=dIodXIa25zp+wFZekGagvKBkctMQIXtfB9VYdRRSLn0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DrpCNgiL8wBGM28isaPW+n9R64QZAm8YYVP9fq4O7J//28WOoLCt0aNjRfC6cxWxlnuYzPxYXhDUhRvrhTqJFcOLYgYR1gdbGdeT65svcATqL7CyWLfXVqFnf/Iujkto9hJGMw/OSDr6FdSjbSKau6BoSw+PlEh3UFfj7ipKF3c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=IR2znhDf; arc=none smtp.client-ip=115.124.30.119 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="IR2znhDf" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1782733118; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=HCQEdys372BeUTJyN2T9I+3CAtzNpqFjiClwous+eV4=; b=IR2znhDf9jw0W02PN2H7aatRGTtORsKI69lD+DIiIsDvw9bxxtRyjJ93ZJ6W2TdTATA2yq6wOYxyXyjlSg9rdax4K+vSqHx7sa6DloRCrEU0zmuVK+WPE0SfBojp902KM+guhbhvEyAc+Ow8LrSUHJFiEkm+dWNzqzWGxXaO4S8= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R751e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045098064;MF=libaokun@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0X5sgdAi_1782733117; Received: from x31h02109.sqa.na131.tbsite.net(mailfrom:libaokun@linux.alibaba.com fp:SMTPD_---0X5sgdAi_1782733117 cluster:ay36) by smtp.aliyun-inc.com; Mon, 29 Jun 2026 19:38:38 +0800 From: Baokun Li To: linux-ext4@vger.kernel.org Cc: tytso@mit.edu, adilger.kernel@dilger.ca, jack@suse.cz, yi.zhang@huawei.com, ojaswin@linux.ibm.com, ritesh.list@gmail.com, peng_wang@linux.alibaba.com Subject: [PATCH v4 2/6] ext4: drain in-flight DIO before buffered write fallback Date: Mon, 29 Jun 2026 19:38:23 +0800 Message-ID: <20260629113827.4074335-3-libaokun@linux.alibaba.com> X-Mailer: git-send-email 2.43.7 In-Reply-To: <20260629113827.4074335-1-libaokun@linux.alibaba.com> References: <20260629113827.4074335-1-libaokun@linux.alibaba.com> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit generic/746 started failing intermittently on ext3 (no-extent inodes). The test triggers 'Page cache invalidation failure on direct I/O' warnings and subsequent fsync returns -EIO. Adding a 50ms delay between ext4_buffered_write_iter() and filemap_write_and_wait_range() in ext4_dio_write_iter() makes the race almost always reproducible. On no-extent inodes, DIO writes to holes cannot use unwritten extents, so ext4_iomap_alloc() leaves m_flags=0 and ext4_map_blocks() returns 0. The iomap layer then returns -ENOTBLK, causing fallback to buffered I/O. The fallback path in ext4_dio_write_iter() calls ext4_buffered_write_iter() which dirties pages, then does flush and invalidate. However, there's an unprotected window between ext4_buffered_write_iter() returning (with inode lock released) and the subsequent flush+invalidate. Concurrent async DIO completions from other threads can run kiocb_invalidate_post_direct_write() during this window. If pages have been re-dirtied, post-invalidation finds dirty pages and triggers the warning, setting -EIO in the error sequence. Consider a file with two 4k extents: [hole][written]. Thread A does DIO to the written extent, while thread B does DIO spanning both: kworker A (4k DIO, allocated block) kworker B (8k DIO, fallback) ----------------------------------- ---------------------------- inode_lock_shared() inode_lock_shared() iomap_dio_rw(): iomap_dio_rw(): kiocb_invalidate_pages -> clean iomap_begin -> -ENOTBLK submit_bio (async) dio->size = 0 inode_unlock_shared() inode_unlock_shared() [bio pending in block layer] /* fallback: lock released */ ext4_buffered_write_iter() inode_lock(exclusive) generic_perform_write() -> dirty pages [0, 8k] inode_unlock(exclusive) /* pages dirty, no lock */ [bio completes] filemap_write_and_wait_range() iomap_dio_complete() -> flush dirty pages kiocb_invalidate_post_direct_write() invalidate_mapping_pages() invalidate_inode_pages2_range() -> finds dirty page! -> dio_warn_stale_pagecache() -> errseq_set(-EIO) This issue can be triggered through normal I/O paths, not just intentionally overlapping DIO writes from userspace. For example, generic/746 uses a loop device where multiple kworkers issue concurrent I/O to the backing file. Additionally, when block_size < folio_size, non-overlapping DIO writes that share a large folio can also trigger the race. Add inode_dio_wait() in ext4_buffered_write_iter() before ext4_write_checks() to drain all in-flight DIO. This ensures that all DIO clears existing pages before submitting IO (via kiocb_invalidate_pages()), all BIO waits for all DIO to complete (via inode_dio_wait()), and ext4_write_checks() observes the inode size after all completed DIO so that ext4_block_zero_eof() does not race with in-flight DIO, thus eliminating the race. Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure") Suggested-by: Zhang Yi Link: https://patch.msgid.link/d1adcf7c-c276-458d-9cac-68a4410f7626@gmail.com Reviewed-by: Zhang Yi Reviewed-by: Jan Kara Signed-off-by: Baokun Li --- fs/ext4/file.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index eb1a323962b1..130edf1ac242 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -309,6 +309,13 @@ static ssize_t ext4_buffered_write_iter(struct kiocb *iocb, return -EOPNOTSUPP; inode_lock(inode); + + /* + * Prevent concurrent direct I/O and buffered I/O to the same file + * range. Wait for in-flight DIO to finish before dirtying pages. + */ + inode_dio_wait(inode); + ret = ext4_write_checks(iocb, from); if (ret <= 0) goto out; -- 2.43.7