From nobody Fri Dec 19 20:06:36 2025 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 8F4AF14EC61; Sun, 24 Mar 2024 23:02:01 +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=1711321322; cv=none; b=EGsj+mls+2/eDhjwOmKzsh/0QSJU7Tlws0BRKoJD+pGDvTQH+OJf9wqKMwdQl6WQhWfsBuFqdV3fdpwJs5JctuHHFOYPIXsKKTQMFUf+ThpTYBljrX3mQ19ERw46JK6zRwg72GHiFpL1Y36H0+A2Cw62/BAFfoaIuMzaVcZ77Fc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711321322; c=relaxed/simple; bh=qOGeOiK4ClElyfszjmQKYlD69NhrO+v312Y/ZK8a4Iw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=I68SFyICkKeQmbAim8UA9VXFineSq/fmFVN20AKvGyiZx1twbgHj4z/prqhvmeDIKtTwzh6TZcccpLlrfYhre/PG+iVyXVlTAPAaSi5tOtPTLWc7f8knVF9VtAO19lkAiGuUtwGFxVCa2086t//vVR50FcpkMcnDfYMF87ZK3Cs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Wmv+j9mc; 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="Wmv+j9mc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE7FAC43390; Sun, 24 Mar 2024 23:02:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711321321; bh=qOGeOiK4ClElyfszjmQKYlD69NhrO+v312Y/ZK8a4Iw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Wmv+j9mcfncsXhnXz+bByTQ+O3E/Ap0ImwzLs+iMLumOZdvpefvBtTLv/MaHkQGIQ 38x+/S9N36xs1Mh77c6CXKSPlCliaG56fEs/OSVMMfDei5GfUY+kluSWadVpmjP45w N6X7Hnkoibuy2n7IS6y8PtBVhVkpJsaO7kTLrYNNysxlFMTcwvTxvHOCGqZVlN9zLV O6xMB2FMEBmHqnTpug4OvlPeKLiAZehZ5wappXmoW2uailwa49F1V2B4ZVPlZRoi58 rohCi6XF6Y4nlp91Ad9OVJ3PYUwOosBT6rqbHZBOKaH91WMd2x4uq+uJP25ZfhiEaI GPJjKZd2U/TCQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Filipe Manana , David Sterba , Sasha Levin Subject: [PATCH 6.6 044/638] btrfs: fix data race at btrfs_use_block_rsv() when accessing block reserve Date: Sun, 24 Mar 2024 18:51:21 -0400 Message-ID: <20240324230116.1348576-45-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240324230116.1348576-1-sashal@kernel.org> References: <20240324230116.1348576-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Filipe Manana [ Upstream commit c7bb26b847e5b97814f522686068c5628e2b3646 ] At btrfs_use_block_rsv() we read the size of a block reserve without locking its spinlock, which makes KCSAN complain because the size of a block reserve is always updated while holding its spinlock. The report from KCSAN is the following: [653.313148] BUG: KCSAN: data-race in btrfs_update_delayed_refs_rsv [btrf= s] / btrfs_use_block_rsv [btrfs] [653.314755] read to 0x000000017f5871b8 of 8 bytes by task 7519 on cpu 0: [653.314779] btrfs_use_block_rsv+0xe4/0x2f8 [btrfs] [653.315606] btrfs_alloc_tree_block+0xdc/0x998 [btrfs] [653.316421] btrfs_force_cow_block+0x220/0xe38 [btrfs] [653.317242] btrfs_cow_block+0x1ac/0x568 [btrfs] [653.318060] btrfs_search_slot+0xda2/0x19b8 [btrfs] [653.318879] btrfs_del_csums+0x1dc/0x798 [btrfs] [653.319702] __btrfs_free_extent.isra.0+0xc24/0x2028 [btrfs] [653.320538] __btrfs_run_delayed_refs+0xd3c/0x2390 [btrfs] [653.321340] btrfs_run_delayed_refs+0xae/0x290 [btrfs] [653.322140] flush_space+0x5e4/0x718 [btrfs] [653.322958] btrfs_preempt_reclaim_metadata_space+0x102/0x2f8 [btrfs] [653.323781] process_one_work+0x3b6/0x838 [653.323800] worker_thread+0x75e/0xb10 [653.323817] kthread+0x21a/0x230 [653.323836] __ret_from_fork+0x6c/0xb8 [653.323855] ret_from_fork+0xa/0x30 [653.323887] write to 0x000000017f5871b8 of 8 bytes by task 576 on cpu 3: [653.323906] btrfs_update_delayed_refs_rsv+0x1a4/0x250 [btrfs] [653.324699] btrfs_add_delayed_data_ref+0x468/0x6d8 [btrfs] [653.325494] btrfs_free_extent+0x76/0x120 [btrfs] [653.326280] __btrfs_mod_ref+0x6a8/0x6b8 [btrfs] [653.327064] btrfs_dec_ref+0x50/0x70 [btrfs] [653.327849] walk_up_proc+0x236/0xa50 [btrfs] [653.328633] walk_up_tree+0x21c/0x448 [btrfs] [653.329418] btrfs_drop_snapshot+0x802/0x1328 [btrfs] [653.330205] btrfs_clean_one_deleted_snapshot+0x184/0x238 [btrfs] [653.330995] cleaner_kthread+0x2b0/0x2f0 [btrfs] [653.331781] kthread+0x21a/0x230 [653.331800] __ret_from_fork+0x6c/0xb8 [653.331818] ret_from_fork+0xa/0x30 So add a helper to get the size of a block reserve while holding the lock. Reading the field while holding the lock instead of using the data_race() annotation is used in order to prevent load tearing. Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/block-rsv.c | 2 +- fs/btrfs/block-rsv.h | 16 ++++++++++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/block-rsv.c b/fs/btrfs/block-rsv.c index 77684c5e0c8ba..db8da4e7b2289 100644 --- a/fs/btrfs/block-rsv.c +++ b/fs/btrfs/block-rsv.c @@ -486,7 +486,7 @@ struct btrfs_block_rsv *btrfs_use_block_rsv(struct btrf= s_trans_handle *trans, =20 block_rsv =3D get_block_rsv(trans, root); =20 - if (unlikely(block_rsv->size =3D=3D 0)) + if (unlikely(btrfs_block_rsv_size(block_rsv) =3D=3D 0)) goto try_reserve; again: ret =3D btrfs_block_rsv_use_bytes(block_rsv, blocksize); diff --git a/fs/btrfs/block-rsv.h b/fs/btrfs/block-rsv.h index fb440a074700a..43a9a6b5a79f4 100644 --- a/fs/btrfs/block-rsv.h +++ b/fs/btrfs/block-rsv.h @@ -117,4 +117,20 @@ static inline u64 btrfs_block_rsv_reserved(struct btrf= s_block_rsv *rsv) return ret; } =20 +/* + * Get the size of a block reserve in a context where getting a stale valu= e is + * acceptable, instead of accessing it directly and trigger data race warn= ing + * from KCSAN. + */ +static inline u64 btrfs_block_rsv_size(struct btrfs_block_rsv *rsv) +{ + u64 ret; + + spin_lock(&rsv->lock); + ret =3D rsv->size; + spin_unlock(&rsv->lock); + + return ret; +} + #endif /* BTRFS_BLOCK_RSV_H */ --=20 2.43.0