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 2546D548EE; Tue, 22 Jul 2025 14:05:46 +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=1753193146; cv=none; b=VR1duiuNgnAqMmvIF1oCaaONY4qa+jdpO8z9TnvMpP67krS72VvMx9a6D1vGJhWuv+hrS6igFy9b14ofdv4Hl04LP+1JDDLxohhmlgxqAuV2kjuXxB0CMJk/egVKNQVSiuneC9LTWJ4GvLZ9nfxplWGpNPsJJia2RemHN+n+apQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753193146; c=relaxed/simple; bh=sQldkDg83g79ElwOD7Fcclsx/Ju5I+F0ffsi4eiq3Pk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=EfifIcqvOPiAd3oo0eX3vfdb3qA39UytQEB1Hn9T+TmZI0lgA0n5MqvE+pBo5zX1T2Z5dTpkBcRD3332X5ostEqW1FkBwfIKWgO9RmyixUJVrYuT5IEHYMBh3/SjfFc74BIpacXSu0sFclLOcDbU1TXybV+u5SIr42QyJ01VeKU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=vXL1hi2j; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="vXL1hi2j" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9FFCFC4CEEB; Tue, 22 Jul 2025 14:05:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1753193146; bh=sQldkDg83g79ElwOD7Fcclsx/Ju5I+F0ffsi4eiq3Pk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vXL1hi2jur+1WDpd27wuOGHXyg7u2IiUlPjkeiwhSvu+Vn2vr59Qy2Sb1TrYcsFeD Lnhb7QFAT03ZJZ4a7TNsK49cHEgiOc33tr6gIRTbDvAr59/pI1/Fy2Kjd8ArT9qtjh +r1Mvh6H6WIZatvudvU9yUjxMRF+FRmMGGt5n8dw= 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 , Alva Lan Subject: [PATCH 6.12 142/158] btrfs: fix block group refcount race in btrfs_create_pending_block_groups() Date: Tue, 22 Jul 2025 15:45:26 +0200 Message-ID: <20250722134346.021137671@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250722134340.596340262@linuxfoundation.org> References: <20250722134340.596340262@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Boris Burkov commit 2d8e5168d48a91e7a802d3003e72afb4304bebfa upstream. 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: Alva Lan Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/block-group.c | 3 +++ 1 file changed, 3 insertions(+) --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c @@ -2780,8 +2780,11 @@ void btrfs_create_pending_block_groups(s /* Already aborted the transaction if it failed. */ next: btrfs_dec_delayed_refs_rsv_bg_inserts(fs_info); + + 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); /* * If the block group is still unused, add it to the list of