From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793214278; b=iG5ssS2qm1svvrKSAaGTWuhS5dbxBdRQD2rdVhU5QAP031yuLxxpHZgGpGP4HKEtW7sd o3Hw6DUuOwaIslhbxpjk/7MWnH/YN/+Z0O/5QpWL5aB0AhAqqAEQzOX/3Hp1/Wu39hJQ3 CMg+mWZkOQr+Kr1kSEm0vuBnbPKc9XsNFScL15qE5RYQwm1k8bs6CKxueTjNqMHXfQGmh cOsysotIs6omfGYiU0XFCbIwfMlJajLyknb55gDhOpN8+X1e1u2vXA9mbW+lCxuEm7AKI 3bQ9rApudDzVk8do2MP5f4iFMAXv+0K04SMJ2tCKT9ntsKFoDux6aU1Z/4toiRywClQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793214278; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=Mh79I7iB3lXL1kMOr8CAHMIJ0mQS2Sh560i8SHxfBAI=; b=zkhPA4lvaFt5i2Il3HEfr9yO6ijtgq78g0hOkUpKjzpzXMVur3ykp/LdyifdtpVdwol0 trpKr8tuRgH5vNSIvYSzl5+hGBFkxaWAnmsF5DPAZVDkCP8SG/FcJ6ieexV8ywsm4sEsa Wo0KrUBhH5AmbHGvAVbb+Ppcw+FbD+1D7RQg5vBmCPBAXXg58iijxxsX8XWpLL4Poyhh9 N1g9TPTzcLZ1lGjeqZKJtb6eTJlQV1yjLNcm4vyU6VSF9mI5YQGy3FBSMvgEAtxmWSAry IKV77LIFn/lT8ICTyL4oAnrmalBiW4zTmlfutcHnRPzfLpnZYNm1i0VahFLDhZH3oPw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=idcadBIX; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5850B60A5BD2; Wed, 28 Oct 2026 19:04:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=idcadBIX Received: by smtp.kernel.org (Postfix) with ESMTPSA id A7F0B1F01825; Wed, 28 Oct 2026 19:04:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793214278; bh=Mh79I7iB3lXL1kMOr8CAHMIJ0mQS2Sh560i8SHxfBAI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=idcadBIXbZiX9ETpQ3I7vviMSY8aIcS3D20a63OvZCJLM/KKO6p7ocFEEpP/4M1uy wsfiZWV0JQ0TjIpEvnA/ofTTMaW29C1DsHqg13R8HOpAo+dV6O2mOEWVwPqCWCUVfh PpuT5GEB/EFJQLq38YOFV3nB2637abyGQpt0eC4U= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Qu Wenruo , Filipe Manana , Boris Burkov , David Sterba , Sasha Levin Subject: [PATCH 6.1 0765/1887] btrfs: fix block group refcount race in btrfs_create_pending_block_groups() Date: Wed, 28 Oct 2026 17:47:41 +0100 Message-ID: <20261028170516.849367977@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170459.200466217@linuxfoundation.org> References: <20261028170459.200466217@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Boris Burkov [ Upstream commit 2d8e5168d48a91e7a802d3003e72afb4304bebfa ] Block group creation is done in two phases, which results in a slightly unintuitive property: a block group can be allocated/deallocated from after btrfs_make_block_group() adds it to the space_info with btrfs_add_bg_to_space_info(), but before creation is completely completed in btrfs_create_pending_block_groups(). As a result, it is possible for a block group to go unused and have 'btrfs_mark_bg_unused' called on it concurrently with 'btrfs_create_pending_block_groups'. This causes a number of issues, which were fixed with the block group flag 'BLOCK_GROUP_FLAG_NEW'. However, this fix is not quite complete. Since it does not use the unused_bg_lock, it is possible for the following race to occur: btrfs_create_pending_block_groups btrfs_mark_bg_unused if list_empty // false list_del_init clear_bit else if (test_bit) // true list_move_tail And we get into the exact same broken ref count and invalid new_bgs state for transaction cleanup that BLOCK_GROUP_FLAG_NEW was designed to prevent. The broken refcount aspect will result in a warning like: [1272.943527] refcount_t: underflow; use-after-free. [1272.943967] WARNING: CPU: 1 PID: 61 at lib/refcount.c:28 refcount_warn_saturate+0xba/0x110 [1272.944731] Modules linked in: btrfs virtio_net xor zstd_compress raid6_pq null_blk [last unloaded: btrfs] [1272.945550] CPU: 1 UID: 0 PID: 61 Comm: kworker/u32:1 Kdump: loaded Tainted: G W 6.14.0-rc5+ #108 [1272.946368] Tainted: [W]=WARN [1272.946585] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014 [1272.947273] Workqueue: btrfs_discard btrfs_discard_workfn [btrfs] [1272.947788] RIP: 0010:refcount_warn_saturate+0xba/0x110 [1272.949532] RSP: 0018:ffffbf1200247df0 EFLAGS: 00010282 [1272.949901] RAX: 0000000000000000 RBX: ffffa14b00e3f800 RCX: 0000000000000000 [1272.950437] RDX: 0000000000000000 RSI: ffffbf1200247c78 RDI: 00000000ffffdfff [1272.950986] RBP: ffffa14b00dc2860 R08: 00000000ffffdfff R09: ffffffff90526268 [1272.951512] R10: ffffffff904762c0 R11: 0000000063666572 R12: ffffa14b00dc28c0 [1272.952024] R13: 0000000000000000 R14: ffffa14b00dc2868 R15: 000001285dcd12c0 [1272.952850] FS: 0000000000000000(0000) GS:ffffa14d33c40000(0000) knlGS:0000000000000000 [1272.953458] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [1272.953931] CR2: 00007f838cbda000 CR3: 000000010104e000 CR4: 00000000000006f0 [1272.954474] Call Trace: [1272.954655] [1272.954812] ? refcount_warn_saturate+0xba/0x110 [1272.955173] ? __warn.cold+0x93/0xd7 [1272.955487] ? refcount_warn_saturate+0xba/0x110 [1272.955816] ? report_bug+0xe7/0x120 [1272.956103] ? handle_bug+0x53/0x90 [1272.956424] ? exc_invalid_op+0x13/0x60 [1272.956700] ? asm_exc_invalid_op+0x16/0x20 [1272.957011] ? refcount_warn_saturate+0xba/0x110 [1272.957399] btrfs_discard_cancel_work.cold+0x26/0x2b [btrfs] [1272.957853] btrfs_put_block_group.cold+0x5d/0x8e [btrfs] [1272.958289] btrfs_discard_workfn+0x194/0x380 [btrfs] [1272.958729] process_one_work+0x130/0x290 [1272.959026] worker_thread+0x2ea/0x420 [1272.959335] ? __pfx_worker_thread+0x10/0x10 [1272.959644] kthread+0xd7/0x1c0 [1272.959872] ? __pfx_kthread+0x10/0x10 [1272.960172] ret_from_fork+0x30/0x50 [1272.960474] ? __pfx_kthread+0x10/0x10 [1272.960745] ret_from_fork_asm+0x1a/0x30 [1272.961035] [1272.961238] ---[ end trace 0000000000000000 ]--- Though we have seen them in the async discard workfn as well. It is most likely to happen after a relocation finishes which cancels discard, tears down the block group, etc. Fix this fully by taking the lock around the list_del_init + clear_bit so that the two are done atomically. Fixes: 0657b20c5a76 ("btrfs: fix use-after-free of new block group that became unused") Reviewed-by: Qu Wenruo Reviewed-by: Filipe Manana Signed-off-by: Boris Burkov Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/block-group.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c index 1f9fbec887c03..a8f096b46b7b2 100644 --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c @@ -2586,8 +2586,11 @@ void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans) /* Already aborted the transaction if it failed. */ next: btrfs_delayed_refs_rsv_release(fs_info, 1); + + spin_lock(&fs_info->unused_bgs_lock); list_del_init(&block_group->bg_list); clear_bit(BLOCK_GROUP_FLAG_NEW, &block_group->runtime_flags); + spin_unlock(&fs_info->unused_bgs_lock); } btrfs_trans_release_chunk_metadata(trans); } -- 2.53.0