From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 45AE843AA8; Mon, 30 Jun 2025 20:58:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751317131; cv=none; b=N+isIN8CG1dh4OiX2Pc29FMnVN96Jo8Fxpi938WQWMg3dI6UPZK6b/HjXvMUZ4dY2ydNz6SMdd/XHBUKd5V7CAWOl3NH8vAJGRU56dOSfIJpn4h48l/aYSbnKRoyhy84osIaFPsYxFhdwxJDiE+bFpKoR2kUbdZzGf2jEUNJQJI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751317131; c=relaxed/simple; bh=RmjfC70IGTG0gB9ct+Smd15Wpijo2sLfeQMmiEV8I3U=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=fxBIDS4wVP1ZKppKPzc95NFe984tMpMc0mSyBK54RT3BcHbX1ApJkq3FGa4+OjgbMNId77E2ltlQdMgSWslmhKYpXdLF5XwnpG2s3T3VEbqE4F6YOIXJiHAtdP9G+Xf1LFwXKabTjQ1Bh+C/Gc9+64kFC6tNrgKqRMloRkpUhiA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=icUIp79t; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="icUIp79t" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F07A9C4CEE3; Mon, 30 Jun 2025 20:58:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1751317130; bh=RmjfC70IGTG0gB9ct+Smd15Wpijo2sLfeQMmiEV8I3U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=icUIp79t9WFABkcopw3DStDe9L49o284gKecKTn1xEZkReSZB5ghboPzXOQ6rfrYR Go0tUMaTOyE1g+9EQJz5FmiySqEzZsAwgpuQqWJWq/n3kjfRUJ6zP3jE4zD7U4Estn Fw+1prCvzmg2uuhVQAkSYxEvfJzFuPyyyX5qk33jxekfJLei9Vy7R5tKydrVD+6Fjs cxW/zb4cx3CdPZpzehssugO+Tbeb8wbrPW7b41jfiFNg77jlw/ShDzIbx7GSaAsTmm D/B5WtWupfcm2F2yRlDamifcUFjXxu3Evsmyw5s3Y6u/ChEoDyy9c0XiTKxI/z0OS8 qek+geiXzp7iQ== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: Fengnan Chang , Jens Axboe , Sasha Levin , asml.silence@gmail.com, io-uring@vger.kernel.org Subject: [PATCH AUTOSEL 6.15 09/23] io_uring: make fallocate be hashed work Date: Mon, 30 Jun 2025 16:44:14 -0400 Message-Id: <20250630204429.1357695-9-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250630204429.1357695-1-sashal@kernel.org> References: <20250630204429.1357695-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.15.4 Content-Transfer-Encoding: 8bit From: Fengnan Chang [ Upstream commit 88a80066af1617fab444776135d840467414beb6 ] Like ftruncate and write, fallocate operations on the same file cannot be executed in parallel, so it is better to make fallocate be hashed work. Signed-off-by: Fengnan Chang Link: https://lore.kernel.org/r/20250623110218.61490-1-changfengnan@bytedance.com Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- **YES** This commit should definitely be backported to stable kernel trees. Here's my extensive analysis: ## Why this is a critical bug fix: 1. **Data Integrity Issue**: The commit fixes a race condition where multiple fallocate operations on the same file could execute in parallel through io_uring. Looking at the implementation in io_uring/sync.c:107, fallocate calls `vfs_fallocate()` which modifies file allocation state. Without proper serialization, concurrent fallocate operations can cause: - Data corruption - Inconsistent file metadata - Filesystem-level race conditions in block allocation 2. **Consistency with Similar Operations**: By examining io_uring/opdef.c, I found that all other file-modifying operations already have `hash_reg_file = 1`: - IORING_OP_WRITEV - IORING_OP_WRITE_FIXED - IORING_OP_WRITE - IORING_OP_SPLICE - IORING_OP_TEE - IORING_OP_FTRUNCATE - IORING_OP_WRITEV_FIXED 3. **Clear Precedent**: When ftruncate support was added in commit b4bb1900c12e, it was correctly implemented with `hash_reg_file = 1` from the start. The fact that fallocate was missing this flag appears to be an oversight that this commit corrects. ## Why it's safe to backport: 1. **Minimal Change**: Single line addition with no architectural changes 2. **Well-Understood Fix**: The `hash_reg_file` mechanism is well- established and used by all similar operations 3. **No Breaking Changes**: The only effect is proper serialization of fallocate operations per-file, which is the correct and expected behavior 4. **Low Risk**: This change cannot introduce new bugs - it only prevents existing race conditions ## How it differs from the "NO" examples: Unlike the provided similar commits which were: - Adding new features (io_uring fallocate support) - Performance optimizations (hashing changes, __read_mostly) - Code cleanup (removing unused fields, refactoring) This commit fixes a **correctness bug** that can lead to data corruption in production systems using io_uring with fallocate operations. The commit follows stable kernel rules perfectly: it's a critical bug fix that's minimal, contained, and addresses a real user-facing issue without introducing new functionality or risks. io_uring/opdef.c | 1 + 1 file changed, 1 insertion(+) diff --git a/io_uring/opdef.c b/io_uring/opdef.c index 489384c0438bd..78ef5976bf003 100644 --- a/io_uring/opdef.c +++ b/io_uring/opdef.c @@ -216,6 +216,7 @@ const struct io_issue_def io_issue_defs[] = { }, [IORING_OP_FALLOCATE] = { .needs_file = 1, + .hash_reg_file = 1, .prep = io_fallocate_prep, .issue = io_fallocate, }, -- 2.39.5