From nobody Mon Feb 9 07:09:34 2026 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 9E879145320; Sun, 24 Mar 2024 23:12:49 +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=1711321969; cv=none; b=MVu6wNOUTtYpgPXIg8iOVXRH9cid8IEIznlNsjjecA0xZ3X6A+9swSbzuWOxnaAPdcxAw5kff1Y9WHg4Uu31DhCc3vnthOqX9iOpbLd7a8CHqVj4BIdjiD2QsJDqUWvjKYL2yhBD+A5agvKrw5hZm2Zb7zvltsHoOAhjoGWCLvg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711321969; c=relaxed/simple; bh=CR7U7I7o3JFIb3W4qXtfs6CITzpzPRT0IhtO4lEfgVQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=gIcmNaggQZd4hrRaMRBRYcIBybR6hhJG8h97HcppqlzOaQYazV4mGKc9eZ9fmCd7xiiiQlU1WGm6b7Qjpy1/IGS9vJwCNxhn4yf2b8SrBZQrEgHZO4a/MMaAw3GPlhR3m0kigXdc6n1hSSZWITOAhR4N2ih8LErBILP51fL63Jw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YLuHa4gn; 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="YLuHa4gn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC55FC43394; Sun, 24 Mar 2024 23:12:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711321969; bh=CR7U7I7o3JFIb3W4qXtfs6CITzpzPRT0IhtO4lEfgVQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YLuHa4gn1mG7BAed7aDUlyeejCt2xqKxqOnfmV51S2BOEQq7MaTX54WvIfmImcGbP CWgFkrmwZeTvqxi/vFS2+5VvCldlB2zyprOw4LQACvZQBEWZ4VL/kj68nnU1z09DAv zxl61+v7vTsAG0uzmgYA8yq6b2KI1PkvkgZMyvX/yvVq5KdukagzUGuxz0w+TugKxX GJXyMaoiZHZiLRQ2denC1np/Ia5FA7SMakHkEQUETB3HN/icTjg58c/BV9DXC9CAXI p3lfB2CJJxKYSstceBEI2YcuPP1qCtjH1phr6UwAWOYC6ESR2ht2gYD/2RtIP4TGx6 W1IISkchrmgGg== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Filipe Manana , David Sterba , Sasha Levin Subject: [PATCH 6.1 041/451] btrfs: fix data race at btrfs_use_block_rsv() when accessing block reserve Date: Sun, 24 Mar 2024 19:05:17 -0400 Message-ID: <20240324231207.1351418-42-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240324231207.1351418-1-sashal@kernel.org> References: <20240324231207.1351418-1-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 507b44d18572d..4cbf386166209 100644 --- a/fs/btrfs/block-rsv.c +++ b/fs/btrfs/block-rsv.c @@ -512,7 +512,7 @@ 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 cda79d3e0c263..df87c4949d065 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